Ink set for inkjet printing

ABSTRACT

An ink set has two or more aqueous pigment-based inks, each of which has 75-95 weight %, a) one or more pigment colorants, and b) one or more water-miscible humectants that are present in a total amount of at least 1 weight % and up to and including 20 weight %, and consist essentially of compounds, each of which has a carbon atom to oxygen atom ratio of at least 1.0:1.0 and only two hydroxy groups. The weight % amounts of water and the b) water-miscible humectants are based on the total weight of each aqueous pigment-based ink. The aqueous pigment-based inks in the ink set can be used individual or in combination to provide monochrome or polychrome inkjet-printed images on various ink-receptive media and using various inkjet printing equipment and methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to the following and commonly assigned patentapplications, the disclosures of all of which are incorporated herein byreference:

U.S. Pat. No. 10,858,529, by Irving and Dannhauser;

U.S. Pat. No. 10,730,331, by Dannhauser and Irving;

U.S. Publication No. 2020/0062017, filed Aug. 21, 2018, by Irving andDannhauser, and recently allowed;

U.S. Ser. No. 16/551,890 filed Aug. 27, 2019, by Lussier, Sowinski,Irving, Putnam, Griffin, and Bugner, and entitled “Method for InkjetPrinting”;

U.S. Ser. No. 16/551,908, filed Aug. 27, 2019, by Irving, Putnam,Sowinski, Lussier, Griffin, and Bugner, and entitled “Article Preparedby Inkjet Printing” and recently allowed;

U.S. Ser. No. 16/551,924, filed Aug. 27, 2019, by Putnam, Irving,Bugner, Sowinski, Griffin, and Lussier, and entitled “Laminated Article”and recently allowed; and

U.S. Ser. No. 16/551,942, filed Aug. 27, 2019, by Putnam, Irving,Bugner, Griffin, Lussier, and Sowinski, and entitled “Method ofPreparing Laminated Article”.

FIELD OF THE INVENTION

This invention relates to the field of inkjet printing using aqueouspigment-based inks applied to ink-receptive media. More particularly, itrelates to an ink set having two or more different aqueous pigment-basedinks that can be used to provide monochrome or polychrome inkjet-printedimages. Each aqueous pigment-based ink has a pigment colorant and aspecific humectant or mixture thereof.

BACKGROUND OF THE INVENTION

High speed digital inkjet printing systems have recently foundconsiderable success in competing with traditional analog printingpresses in applications such as commercial printing and publishing. Inparticular, inkjet printing systems that employ aqueous pigment-basedinks can rival the print quality and productivity of printing systemsthat are based on analog impact printing, such as lithography, gravure,and flexographic printing systems. The ability of digital inkjetprinting systems to print either short-run lengths or continuouslyvariable information in a cost-effective manner offers distinctadvantages over such traditional impact printing systems that requirethe presses to be idled between print jobs.

More recently, high productivity digital inkjet printing systems havebeen targeted toward décor and packaging printing, with the sameadvantages. However, such printing, unlike commercial printing andpublishing, typically employ water-impermeable substrates such aspolymeric films, metal foils, and glass, in addition to paper-basedsubstrates on which images are printed. Plastic substrates areparticularly challenging for the use of aqueous pigment-based inks dueto the difficulty in getting such inks to wet and adhere to suchsubstrates that are typically designed and chosen to repel or otherwisepresent a barrier to water. Although solvent-based and radiation-curable(for example UV-curable) inkjet inks have been used with some success onplastic substrates, their use is limited to certain types of inkjetprinting systems, such as piezoelectric drop-on-demand (DOD) systems andthey present some health, safety, and environmental concerns compared tothe use of aqueous-based inks.

When aqueous-based inks are used in high-speed digital inkjet printing,especially inks that contain more than 80 weight % of water and lessthan 15 weight % of organic co-solvents (also known as “humectants”) anddeposited on commonly available plastic substrates used for décor andpackaging application, the ink drops tend to either bead up or flowacross the substrate surface, resulting in significant defects known asmottle, coalescence, and intercolor bleeding. In addition, such inks aredifficult to dry quickly due to the presence of the co-solvents,resulting in a very sticky or tacky printed layer or image.

The literature has proposed a number of ways to overcome the notedproblems, for example, the incorporation of additives into the inks thatchange their viscosity when heated on the plastic substrate; theaddition of polymer particles to fuse during heating after printing; theheating of the ink containing mixtures of co-solvents during printing;the use of a “fixing” fluid and ink with specific co-reactive polymers;the use of an adhesive layer on the water-impermeable substrate surface;the surface treatment of the water-impermeable substrate prior to inkjetprinting, including the use of protective overcoats; and the use ofhigh-boiling co-solvents in “fixing” fluids to modify the substratesurface.

It is also well known to deposit aqueous pigment-based inks onto asubstrate having cations of a multivalent metal salt on the surfacethereof. The presence of such multivalent metal cations can be used toprevent deposited ink drops from penetrating too far below the surfaceof a water-absorptive substrate, thereby preventing a lowering ofoptical density. The multivalent metal cations can also be used toprevent bleeding or coalescing of adjacent deposited ink drops of thesame or different colors on a less absorbent substrate such as awater-impermeable substrate, thereby preventing the formation of blurryor grainy appearing images. Surface treatments comprising aqueous saltsof multivalent metal ions are particularly advantageous for high speedprinting with page-wide inkjet arrays whereby adjacent drops of ink aredeposited within just a few microseconds of each other onto thesubstrate.

U.S. Pat. No. 9,434,201 (Dannhauser et al.) describes inkjet receivingmedia suitable for high speed inkjet printing, which media include asubstrate having a topmost layer coated thereon comprising an aqueoussoluble salt of a multivalent metal cation and a cross-linkedhydrophilic polymer binder.

In U.S. Patent Application Publication 2011/0279554 (Dannhauser et al.),it is proposed to modify water-impermeable substrates by applying apre-coating composition comprising water-soluble salts of multi-valentmetal cations in combination with hydrophilic binders. While applicationof such pre-coats can improve the adhesion of aqueous pigment-based inksduring high-speed inkjet printing, the adhesion and wetting may needimprovement. Moreover, high-boiling co-solvents or humectants present insuch aqueous pigment-based inks cannot readily penetrate into thesubstrate, leading to prolonged tackiness in the resulting printedimage.

U.S. Pat. No. 8,562,126 (Xiang et al.) describes pre-treatment ofglossy, semi-glossy, and matte-coated paper substrates for inkjetprinting using a coating composition containing an aqueous salt of amulti-valent metal cation, a polyelectrolyte comprising amidinemoieties, and another polymer such as a polyamide-epichlorohydrin, apolyamine solution polymer, or a water-based polyurethane. Waxes can beadded to such compositions as described in U.S. Patent ApplicationPublication 2003/0203134 (Sheng).

U.S. Pat. No. 9,376,582 (Dannhauser et al.) and U.S. Pat. No. 9,573,349(Dannhauser et al.) provide a solution to the noted problems with amulti-structural substrate having a water-impermeable support (such as athin plastic film), a first layer that contains a water-based tie-layercomposition, and a second layer (aqueous-based ink-receptive layer)containing an aqueous-soluble salt of a multivalent cation and ahydrophilic binder polymer. One or more aqueous pigment-based inks canbe applied to this multi-structural substrate to form an inkjet printedimage, particularly when the pigments are anionically-stabilized andwater-dispersible pigments. Additional layers can be applied to theinkjet printed images if desired. In particular, it can be advantageousto add an adhesive layer to the inkjet printed image so that anotherwater-impermeable film can be laminated thereto to produce laminatedflexible packaging with an “embedded” inkjet printed image.

However, it has been found recently that when the aqueous pigment-basedinks used in these methods and with such multi-structural substrates,which contain certain humectants well known in the art, the finallaminated flexible packaging material exhibits poor lamination bondstrength and delamination can occur. There is a need to solve thisproblem without sacrificing high-speed inkjet printing and essentialoperational properties such as stable and accurate jetting, highproductivity, machine throughput, and printed image quality. There isalso a need to improve the adhesion of the aqueous-based ink-receptivelayer directly to a water-impermeable substrate, thereby eliminating theneed for a separate water-based tie-layer composition as required in themulti-layer structures methods disclosed in U.S. Pat. Nos. 9,376,582 and9,573,349 (both noted above).

SUMMARY OF THE INVENTION

The present invention provides an ink set comprising two or moredifferent aqueous pigment-based inks, each aqueous pigment-based inkhaving at least 75 weight % and up to and including 95 weight % ofwater, and comprising:

a) one or more pigment colorants;

b) one or more water-miscible humectants that are present in a totalamount of at least 1 weight % and up to and including 20 weight %, andconsist essentially of compounds, each of which has a carbon atom tooxygen atom ratio of at least 1.0:1.0 and only two hydroxy groups;

and optionally,

c) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, and each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink,

wherein the weight % amounts of water and the b) water-misciblehumectants are based on the total weight of each aqueous pigment-basedink.

In addition, the present invention provides ink set embodiments, eachcomprising two or more aqueous pigment-based inks, each aqueouspigment-based ink having at least 75 weight % and up to and including 90weight % of water, and comprising:

a) one or more pigment colorants, wherein 50% of the volume of each ofthe a) one or more pigment colorants is provided by pigment colorantparticles having a diameter of less than 100 nm, and 95% of the volumeof each of the a) one or more pigment colorants is provided by pigmentcolorant particles having a diameter of less than 150 nm, the particlesize diameters being measured using a dynamic light scattering particlesizing instrument;

b) one or more water-miscible humectants defined as follows for eachindividual aqueous pigment-based ink; and

c) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink;

wherein the two or more aqueous pigment-based inks are selected from thefollowing:

an aqueous cyan pigment-based ink that comprises one or moreanionically-stabilized cyan pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %;

an aqueous magenta pigment-based ink that comprises one or moreanionically-stabilized magenta pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %;

an aqueous yellow pigment-based ink that comprises one or moreanionically-stabilized yellow pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol,ethylene glycol, diethylene glycol, or a combination of two or more ofthese compounds, in a total amount of at least 4 weight % and up to andincluding 8 weight %; and

an aqueous black pigment-based ink that comprises one or moreanionically-stabilized black pigment colorants, and the b) one or morewater-miscible humectants consists essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 5 weight % and up to and including 10 weight %,

all amounts being based on the total weight of the respective aqueouspigment-based ink.

The present invention provides a solution to the delamination problemdescribed above. Modification of the aqueous-based ink-receptive layerimproves its capability to absorb residual humectants of specificclasses from the aqueous pigment-based inks after drying, therebyimproving lamination bond strength. At the same time, the improvedaqueous-based ink-receptive layer provides the option of omittingwater-based “tie” layers from between a water-impermeable substrate andan inkjet printed image. Minimization or exclusion of certain commonhumectant compounds from, and inclusions of other specific humectantcompounds within, the aqueous pigment-based inks also improveslamination bond strength. Specifically, the present invention utilizesonly dihydroxy humectants in which the carbon atom to oxygen atom molarratio is at least 1.0:1.0 and up to and including 2.7:1.0, and1,2,3-trihydroxypropane (glycerol) is used as little as possible, oromitted entirely. The dihydroxy humectants with carbon atom to oxygenatom molar ratio of at least 1.0:1.0 simultaneously provide aqueouspigment-based inks that exhibit stable jet formation without sufferingink drying on the printhead nozzle plate, which problem produces blockednozzles, crooked jets and ragged jet curtains, or poor printheadstart-ups after extended shutdowns. Stable and robust drop formation isessential for accurate printing without interference from excessiveprinthead maintenance service cycles. These features are described inmore detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial cross-sectional view of a simple embodiment of anaqueous-based ink receiving medium used in the practice of the presentinvention.

FIG. 2 shows a partial cross-sectional view of still another embodimentof an aqueous-based ink receiving medium used in the practice of thepresent invention comprising multiple layers.

FIG. 3 shows a partial cross-sectional view of one embodiment of aninkjet-printed article according to the present invention.

FIG. 4 shows a partial cross-sectional view of one embodiment of aflexible inkjet-printed article according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is directed to various embodiments of thepresent invention and while some embodiments can be desirable forspecific uses, the disclosed embodiments should not be interpreted orotherwise considered to limit the scope of the present invention, asclaimed below. In addition, one skilled in the art will understand thatthe following disclosure has broader application than is explicitlydescribed in the discussion of any specific embodiment.

Definitions

As used herein to define various components of aqueous pigment-basedinks, aqueous-based ink-receptive layers, inkjet printed images orlayers, functional layers, and other materials used in the practice ofthis invention, unless otherwise indicated, the singular forms “a,”“an,” and “the” are intended to include one or more of the components(that is, including plurality referents).

Each term that is not explicitly defined in the present application isto be understood to have a meaning that is commonly accepted by thoseskilled in the art. If the construction of a term would render itmeaningless or essentially meaningless in its context, the term shouldbe interpreted to have a standard dictionary meaning.

The use of numerical values in the various ranges specified herein,unless otherwise expressly indicated otherwise, are to be considered asapproximations as though the minimum and maximum values within thestated ranges were both preceded by the word “about.” In this manner,slight variations above and below the stated ranges may be useful toachieve substantially the same results as the values within the ranges.In addition, unless otherwise indicated, the disclosure of these rangesis intended as a continuous range including every value between theminimum and maximum values as well as the end points of the ranges.

As used herein, the parameter “acid number” (also known as acid value)is defined as the milligrams (mg) of potassium hydroxide required toneutralize 1 g of the described acidic polymer.

The term “aqueous” in aqueous organic pigment dispersions, aqueouscompositions, and aqueous (anionically-stabilized) pigment-based inksaccording to the present invention means that the water content isgreater than 60 weight %, or at least 80 weight % based on the totalweight of all solvents. Thus, water is the predominant solvent in suchformulations.

The terms “water-soluble” and “aqueous-soluble” mean that 1 mass part ofsolute material can be dissolved in as little as less than 1 mass part(that is, more soluble solute) and in as much as 1,000 mass parts (thatis, less soluble solute) of distilled water at 25° C. to provide ahomogeneous and visibly clear solution.

The term “humectant” is defined as a water-miscible co-solvent thatslows down the rate of evaporation of an aqueous-based ink, therebydelaying insolubilization or precipitation of the solid components ofthe ink. As such, a humectant has a higher boiling point and a lowervapor pressure at a given temperature than water such that it is moredifficult to evaporate than water. Thus, humectants are water misciblepolar organic compound (typically a low volatility solvent having aboiling point at sea level near or greater than about 200° C.), or acombination of such compounds, that retards water evaporation from anaqueous-based ink to reduce printhead jetting failures due to blockednozzles or crooked jets resulting from the formation of dried inkdeposits.

Aqueous pigment-based ink and fluid dynamic viscosity can be measured byany of well-known techniques. Preferred methods include measurement ofthe timing of mass flow through a capillary as in a capillaryviscometer, or measurement of ball drop velocity through a fluid, usingfor example a rolling ball viscometer. Both a capillary flow viscometerand a commercially available Anton Paar Automated MicroViscometer (AMVn)employing the rolling ball technique can be used to measure the dynamicviscosities reported herein. All aqueous pigment-based ink dynamicviscosity values disclosed herein were measured under gravity inducedshear at approximately 24° C. to 26° C. It will be appreciated that thevalues cited are reported as centipoise (cP) or millipascal seconds(mPa-sec) and that 1 cP=10⁻³ Pascal-seconds (Pa-s) equals 10⁻²dyne-s/cm². While viscosities can be measured with high precision,viscosity values here are reported to one or two decimal places only,and they are normally rounded values and not truncated values. Allclaims reciting aqueous pigment-based ink viscosities are intended to beinterpreted in terms of values in mPa-sec normally rounded to onedecimal point. Thus, the various aqueous pigment-based inks can have adynamic viscosity of up to and including 10 centipoise (10 mPa-sec), butmore likely the values described below.

The Wilhelmy plate method is a well-known technique for measuring thestatic surface tension of an aqueous pigment-based ink or service fluidat a solid interface. The technique involves a plate of knowndimensions, typically selected from a roughened platinum alloy,suspended from a balance. The plate is contacted with a solution ofinterest and a vertical force is applied to the plate to form a liquidmeniscus between the solution and plate. The resulting surface tensionis given according to equation (1):σ=F/L cos(θ)  (1)where σ is the surface tension of the liquid, F is the force acting onthe balance (milli-Newtons/meter), L is the wetted length of the platein millimeters, and θ is the contact angle between the plate andsolution.

Typically, the roughened platinum results in a contact angle very closeto zero and the cosine of θ goes to 1. A complete theoretical treatmentof the method can be found in, for example, “A Method for DeterminingSurface and Interfacial Tension Using a Wilhelmy Plate,” Colloid andPolymer Science, 255 (7), pages 675-681. A number of commerciallyavailable instruments are known for measuring surface tension, however,the instrument used to report surface tension values in the presentinvention is a Krüss Model K10ST tensiometer.

Particle size for the various a) pigment colorants (includinganionically-stabilized pigment colorants) refers to the approximatediameter of a generally spherical pigment particle or to the approximatelargest characteristic dimension of a non-spherical particle. The95^(th) percentile particle size refers to the classified particle sizedistribution such that 95% of the pigment colorant particles is providedby particles having diameters smaller than the indicated diameter.Similarly, the 50^(th) percentile particle size (or median particlesize) refers to the classified particle size distribution such that 50%of the pigment colorant particles is provided by particles havingdiameters smaller than the indicated diameter. Such particle sizemeasurements can be made using either laser diffraction (static)techniques or dynamic light scattering techniques. Laser diffractiontechniques will provide a “volume” weighted particle size distribution,whereas dynamic light scattering techniques will provide an “intensity”weighted distribution. For the particle size distributions reportedbelow in the working examples, a Nanotrac 150 NPA ultrafine particleanalyzer (Microtrac, Inc.) was used. This is a dynamic light scatteringdevice, and standard procedures for using such a device are described inNational Institute of Standards and Technology (NIST) SpecialPublication 1200-6, Measuring the Size of Nanoparticles in Aqueous MediaUsing Batch-Mode Dynamic Light Scattering NIST-NCL Joint Assay Protocol,PCC-1 Version 1.2, May 2015 and in ISO 22412:2017 Particle SizeAnalysis-Dynamic Light Scattering (DLS). This dynamic light scatteringdevice can be used to measure particle size distributions in “intensity”mode, but it is also capable of being used to calculate and report the“volume” mode particle size distributions for comparative purposes.

As used herein, “ink set” refers to two or more different aqueouspigment-based inks that can be sold or supplied in separate containersof the same or different sizes by a manufacturer or vendor. An ink setalso refers to the collection of aqueous pigment-based inks and anyclear fluids that are used in individual fluid supplies (or reservoirs)incorporated into specific inkjet printing equipment that are designedfor accommodating a specific volume of each aqueous pigment-based ink.An ink set can also be identified with a unique catalog number for sale,or the ink set can be assembled by a supplier or user from individualaqueous pigment-based inks having individual catalog numbers.

For clarification of definitions for any terms relating to polymers,reference should be made to “Glossary of Basic Terms in Polymer Science”as published by the International Union of Pure and Applied Chemistry(“IUPAC”) in Pure Appl. Chem. 68, 2287-2311 (1996). However, anydefinitions explicitly set forth herein should be regarded ascontrolling.

As used herein, the terms “polymer” and “polymeric” refer to bothhomopolymers and copolymers, each having a stated weight distributionaverage molecular weight (M_(w)) as measured using gel permeationchromatography (polystyrene standard).

The term “copolymer” refers to polymers derived from two or moredifferent monomers that provide two or more different repeating orrecurring units of different chemical structures arranged, in randomorder or predetermined order, along the polymer backbone. The term“backbone” refers to the chain of atoms in a polymer to which aplurality of pendant groups can be attached. An example of such abackbone is an “all carbon” backbone obtained from the polymerization ofone or more ethylenically unsaturated polymerizable monomers. However,other backbones can include heteroatoms wherein the polymer is derivedby condensation reactions or some other means.

The a) pigment colorants used in the various embodiments of the presentinvention are not generally self-dispersing, meaning that they requirethe presence of one or more organic polymeric pigment dispersants boundto some fraction of the surface of the pigment particles to keep themsuspended in an aqueous medium, but suitable self-dispersed pigmentedcolorants can readily be employed in the practice of the invention.

The term “weight %” of an aqueous pigment-based ink component within thecomposition is the ratio of the weight of that component to the totalweight of the composition (the weight fraction) multiplied by 100 inorder to be expressed as percentage by weight (parts per 100), sometimesabbreviated as wt. % or as w/w %. It is a convenient way of expressingthe composition of a mixture in a dimensionless size.

As used herein, the term “layer” or “coating” can consist of onedisposed or applied layer or a combination of several sequentiallydisposed or applied layers, such as sub-layers.

As used herein in reference to various materials used in supports,substrates, or layer, the term “water-impermeable” refers to a watervapor transmission (WVTR) rate of less than about 500 g/m²/day/bar at38° C. and 90% RH, as measured by test cells and instrumentation inaccord with, for example, ASTM F1249, for measuring the WVTR of plasticfilms.

Uses

The aqueous pigment-based inks (including aqueous anionically-stabilizedpigment-based inks), inkjet-printed articles, and flexibleinkjet-printed articles according to the present invention can be usedin or prepared using aqueous inkjet printing methods, including thoseutilizing continuous inkjet printing apparatus and systems described inmore detail below. The resulting articles can be used in any suitablemanner where inkjet-printed images are needed, including but not limitedto flexible packaging materials and décor materials used in variousindustries.

Aqueous-Based Ink-Receptive Layer and Aqueous Compositions

The aqueous-based ink-receptive layer compositions (or “aqueouscompositions” hereinafter) used to provide aqueous-based ink-receptivelayers according to the present invention generally have at least 2%solids and up to and including 50% solids, or even at least 4% solidsand up to and including 25% solids, the rest of the aqueous compositionbeing predominantly a solvent medium consisting essentially of water asdescribed below. The various “dry” amounts of the components describedbelow can be achieved using appropriate amounts of those components inthe aqueous compositions in view of the noted % solids.

The aqueous compositions must comprise one or more (a) water-solublesalts of multivalent metal cations as a first essential component.Mixtures of such salts having the same multivalent metal cation, andmixtures of salts having different multivalent cations can be used, inany desired proportion. Generally, each of these salts is colorless andnon-reactive with other materials in the aqueous compositions. Forexample, such salts can comprise one or more multivalent cations such asmagnesium (+2), calcium (+2), barium (+2), zinc (+2), or aluminum (+3).The magnesium (+2) and calcium (+2) cations are particularly useful, incombination with suitable counterions.

Examples of useful (a) water-soluble salts of a multivalent metal cationinclude but are not limited to, calcium chloride, calcium acetate,calcium nitrate, magnesium chloride, magnesium acetate, magnesiumnitrate, barium chloride, barium nitrate, zinc chloride, zinc nitrate,aluminum chloride, aluminum hydroxychloride, and aluminum nitrate.Hydrated versions of these salts can also be used. Other useful saltswould be readily apparent to a skilled artisan. Particularly usefulwater-soluble salts of a multivalent metal cation comprise one or moreof CaCl₂), Ca(CH₃CO₂)₂, MgCl₂, Mg(CH₃CO₂)₂, Ca(NO₃)₂, and Mg(NO₃)₂, andhydrated versions of these salts. Such materials can be obtained fromvarious commercial sources.

The amount of the (a) water-soluble salts of multivalent metal cationsin the aqueous composition can be determined using routineexperimentation to obtain a dry aqueous-based ink-receptive layer amountof at least 0.6 weight % or at least 1 weight %, and up to and including24 weight %, or even up to and including 49 weight %, all based on thetotal weight of the aqueous-based ink-receptive layer from which thesolvent medium has been removed. For example, it is useful to providethe (a) one or more water-soluble salts of a multivalent metal in theaqueous-based ink-receptive layer in an amount of at least 0.01 g/m² andup to and including 1 g/m².

The amount of the (b) one or both of a polyvinyl alcohol and a polyvinylamine, or a copolymer derived from a vinyl alcohol and a vinyl amine, asanother essential component in the aqueous composition can also bedetermined using routine experimentation to obtain a dry aqueous-basedink-receptive layer amount of at least 0.5 weight %, or at least 1weight %, and up to and including 20 weight %, or up to and including 30weight %, based on the total weight of the aqueous-based ink-receptivelayer. These amounts refer to the total amount of all of the polyvinylalcohol and polyvinyl amine that are present. Such materials aregenerally capable of absorbing water and of forming a continuous phasesolution.

The term “polyvinyl alcohol” is meant to include a polymer of variousweight average molecular weights having the —CH(OH)—CH₂— recurring unitas well as modified polyvinyl alcohols or derivatives of polyvinylalcohol in which the hydroxy group of one or more recurring units hasbeen replaced with a different organic moiety (thus, a modifiedrecurring unit). Such materials include but not limited to anacetylacetate-modified poly(vinyl alcohol), ethylene oxide-modifiedpoly(vinyl alcohol), polyvinyl butyral derivatives, polyvinyl formalderivatives, any other materials that would be readily apparent to oneskilled in the art from this teaching. Such polymers can be derived fromone or more vinyl alcohol monomers (or derivatives thereof) or they canbe derived from the vinyl alcohol monomer that is then modified afterpolymerization. While some useful polyvinyl alcohols are crosslinkable,others are not. In crosslinked form, such materials provide resistanceto abrasion in the wet formulation and increased cohesion in a drycoating.

Useful polyvinyl alcohols generally have a weight average molecularweight (M_(w)) of at least 3,000 and up to and including 150,000.

Useful polyvinyl alcohols are available from various commercial sourcesunder various tradenames such as ELVANOL™, GOHSENOL™, and EXCEVAL™.

The term “polyvinyl amine” refers to polymers having —CH(NH₂)CH₂—recurring units. Useful materials are available, for example, from BASFAktiengesellschaft under the tradename LUPAMIN™. Such polymers can bederived from a vinyl amine monomer or modified monomers.

Moreover, useful polyvinyl amines generally have a weight averagemolecular weight (M_(w)) of at least 10,000 and up to and including1,000,000.

In some embodiments, it is desirable that the weight ratio of theessential (a) one or more water-soluble salts of a multivalent metalcation to the essential (b) one or more of a polyvinyl alcohol and apolyvinyl amine is from 0.02:1 to and including 100:1, or from 0.1:1 to50:1.

Moreover, in some embodiments, both a polyvinyl alcohol and a polyvinylamine are present in the aqueous-based ink-receptive layer, in a weightratio of the polyvinyl alcohol to the polyvinyl amine of from 0.1:1, orto a copolymer derived from a vinyl alcohol and a vinyl amine (asdescribed below), to and including 20:1, or from 0.5:1 to and including10:1.

Also useful are copolymers, each of which is derived from a monomermixture of a vinyl alcohol monomer as defined above (or a mixture ofsuch monomers) and a vinyl amine as defined thereof (or a mixture ofsuch monomers) to produce the desired —CH(OH)—CH₂— (or modifiedrecurring unit as described above) and —CH(NH₂)CH₂— recurring units inthe copolymer. The molar ratios of the various monomers and recurringunits can be adjusted using known skill and routine experimentation toachieve the desired results in the aqueous-based ink-receptive layer.Mixtures of such copolymers can be used if desired. One or morecopolymers can be used in combination with a polyvinyl alcohol orpolyvinyl amine, as they are defined above.

It may be useful to include one or more (c) crosslinking agents in theaqueous composition to promote crosslinking of one or both of thepolyvinyl alcohol and polyvinyl amine, or of other materials that arepresent. However, while such (c) crosslinking agents are desirable, theyare optional. The identity and amount of crosslinking agent will dependupon the choice and amount of crosslinkable material present and itsreactivity with the crosslinking agent, the number of crosslinking sitesavailable, its compatibility with other materials in the aqueouscomposition, and manufacturing constraints such as solution pot life andcoating drying speed. Representative crosslinking agents include but arenot limited to, glyoxal, CARTABOND® TSI and EPI (Clariant), SEQUAREZ®755 (Omnova), glutaraldehyde sodium bisulfate complex (Aldrich), Sunrez700 M and 700C (Omnova), bis(vinyl) sulfone), bis(vinyl)sulfone methylether, adipoyl dihydrazide, epichlorohydrin polyamide resins, andurea-formaldehyde resin. Useful crosslinking agents can be obtained fromvarious commercial sources.

The one or more (c) crosslinking agents can be present in theaqueous-based ink-receptive layer in a dry layer amount of at least 0.01weight % or of at least 0.1 weight %, and up to and including 2 weight %or up to and including 5 weight %, based on the total weight of theaqueous-based ink-receptive layer. Routine experimentation can becarried out by a skilled artisan to determine the amount of one or more(c) crosslinking agents to include in an aqueous composition to obtainthe desired “dry” amounts.

It is also optional but desirable to include one or more types of (d)silica particles in the aqueous composition in a dry layer amount of upto 10 weight % or up to and including 30 weight %, based on the totalweight of the aqueous-based ink-receptive layer. The minimum amountpresent can be at least 1 weight % or even at least 5 weight %. Forexample, silica gel, silica (such as fumed silica or colloidal silica)can be present. Such materials can be obtained from various commercialsources. A skilled artisan would know from these amount using routineexperimentation how much of the silica particles to include the aqueouscomposition.

The aqueous composition (and resulting aqueous-based ink-receptivelayer) can also contain various other addenda that would provide certaindesirable properties, including wax particles as known in the art. Inaddition, the aqueous composition (and resulting aqueous-basedink-receptive layer) can include the composite particles described incommonly assigned U.S. Ser. No. 16/106,033 noted above, in the amountsdescribed therein, the disclosure of which is incorporated herein byreference.

The aqueous compositions can be prepared by suitably mixing the variousessential and optional materials described above in any desired mixingorder and with suitable equipment, in a solvent medium that ispredominantly water. At least 60 weight %, or even at least 80 weight %and up to and including 100 weight %, of the solvent medium is comprisedof water, based on the weight of all solvents. The possible % solids isnoted above.

The aqueous composition used in the practice of this invention can havea dynamic viscosity, measured at 25° C. using a standard rolling ballviscometer, of less than or equal to 200 centipoise (200 mPa-sec), ofless than or equal to 50 centipoise (50 mPa-sec), or of less than orequal to 20 centipoise (200 mPa-sec) for appropriate coating such asusing a CIJ printing system described below.

Preparation of suitable aqueous-based ink-receptive layers are describedbelow using appropriate aqueous compositions. Desirably, the drycoverage of the aqueous-based ink-receptive layer is at least 0.3 g/m²or at least 0.75 g/m² and up to and including 1.5 g/m² or up to andincluding 3 g/m².

Representative aqueous compositions and their use according to thepresent invention are described below within the working Examples.

Aqueous Pigment-Based Inks and Ink Sets

The methods and articles according to the present invention can beaccomplished using a single aqueous pigment-based ink, or by usingmultiple different aqueous pigment-based inks, including the two or moredifferent aqueous pigment-based inks (of the same or different hue) thatcan be supplied to a user as part of an ink set according to the presentinvention.

Each aqueous pigment-based ink useful according to the present inventioncan be prepared from a suitable aqueous dispersion of a) one or morepigment colorants using known dispersants and dispersing means. Theresulting dispersed pigment colorants can be mixed with the b) one ormore water-miscible humectants (identified below) and optional c) acidicpolymer and other additives described below, and all components areformulated within an aqueous medium (predominantly water) to provide anink formulation having a dynamic viscosity of at least 1 centipoise (1mPa-sec) and up to and including 10 centipoise (10 mPa-sec), or lessthan or equal to 5 centipoise (5 mPa-sec), or less than or equal to 3centipose (3 mPa-sec), or even less than 1.5 centipoise (1.5 mPa-sec),all measured at 25° C. as described above.

In many embodiments according to the present invention, the a) one ormore pigment colorants used according to the present invention can be“anionically-stabilized” as described below, and thus, the resultingformulations are “aqueous anionically-stabilized pigment-based inks.” Inthe following discussion, the a) one or more pigment colorants can be a)one or more anionically-stabilized pigment colorants using stabilizingdispersants or compounds such as anionic polymer or non-polymericstabilizers, or they can be stabilized with anionic stabilizing groupson the surface of the pigment particles (“self-dispersed”).

Organic anionic polymer dispersed pigment colorants are useful in thepractice of this invention and can be used singly, or in combinations oftwo or more different organic polymers or otherwise-dispersed pigmentcolorants, to provide any desired color or hue.

The exact choice of a) one or more pigment colorants will depend uponthe specific application, performance, color reproduction, and imagestability that are desired. Useful organic polymer-dispersed pigmentcolorants are described for example in U.S. Pat. No. 5,026,427 (Mitchellet al.), U.S. Pat. No. 5,141,556 (Matrick), U.S. Pat. No. 5,160,370(Suga et al.), and U.S. Pat. No. 5,169,436 (Matrick), the disclosures ofall of which are incorporated herein by reference.

Useful a) one or more pigment colorants that can be dispersed withorganic polymers include but are not limited to, azo pigments, monoazopigments, disazo pigments, azo pigment lakes, β-naphthol pigments,naphthol AS pigments, benzimidazolone pigments, disazo condensationpigments, metal complex pigments, isoindolinone and isoindolinepigments, quinacridone pigments, polycyclic pigments, phthalocyaninepigments, perylene and perinone pigments, thioindigo pigments,anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments,dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments,diketopyrrolo pyrrole pigments, titanium dioxide, iron oxide, and carbonblacks. Representative a) one or more pigment colorants are described inCol. 7 (line 48) to Col. 8 (line 5) of U.S. Pat. No. 8,173,215 (Sowinskiet al.), the disclosure of which is incorporated herein by reference.

Useful a) one or more pigment colorants can be accompanied or dispersedusing suitable polymer dispersants that are well known in the art (ascited above). Representative useful anionic organic polymer dispersantscan be prepared from at least one anionic hydrophilic monomer such as anacrylic acid or methacrylic acid monomer, or combinations thereof, andfor example, at least one monomer comprised of a hydrophobicmethacrylate or acrylate monomer having an aliphatic chain having 12 ormore carbon atoms, as described for example in U.S. Patent ApplicationPublication 2007/0043144 (House et al.), the disclosure of which isincorporated herein by reference. Further details of useful organicpolymer dispersants, including useful monomer recurring units, monomeramounts, and M_(w), are provided in Col. 5 (line 45) to Col. 6 (line 31)of U.S. Pat. No. 8,173,215 (noted above). For example, many usefulorganic (anionic) polymer dispersants are anionic acrylic polymersformed from at least one anionic hydrophilic monomer described abovehaving a weight average (M_(w)) molecular weight of at least 500 Daltonsbut less than 100,000 Daltons, and more likely up to and including15,000 Daltons, or up to and including 10,000 Daltons.

One or more organic polymer dispersants for the a) one or more pigmentcolorants can be present in an amount that would be readily apparent toone skilled in the art depending upon the aqueous medium, the chosenparticulate colorants, and other components of the aqueous pigment-basedink.

In addition to the polymeric dispersants, nonionic or anionicsurfactants can be present with the a) one or more pigment colorants asis known in the art. Representative materials of this type include butare not limited to, sodium dodecylsulfate or sodium oleylmethyltaurateas described for example in Col. 7 (lines 15-23) of U.S. Pat. No.8,173,215 (noted above).

Each aqueous pigment-based ink useful in the practice of this inventiontypically comprises a) one or more pigment colorants that will providethe desired color or hue such as black, green, red, yellow, blue,violet, magenta, cyan, white, brown, grey and other hues known orachievable using known color blending technology. Desired colors can beobtained using a) one or more pigment colorants that are designed toabsorb electromagnetic radiation so that specific a* and b* CIELABchromaticity parameters are met to provide a desired hue. Thus, pigmentcolorants can be present individually or in mixtures in each aqueouspigment-based ink. For example, individual aqueous pigment-based inksuseful in the present invention can comprise a) one or more pigmentcolorants selected from a cyan pigment, a magenta pigment, a yellowpigment, a black pigment, a green pigment, an orange pigment, a whitepigment, a red pigment, a blue pigment, a violet pigment, and acombination of any of these pigment colorants, any and all of which canbe anionically-stabilized pigment colorants for example using anionicorganic polymer stabilizers.

Some organic and inorganic a) one or more pigment colorants can be usedcombination. For example, a carbon black pigment can be combined with adifferently colored pigment such as a cyan copper phthalocyanine or amagenta quinacridone pigment. A combination of yellow and green pigmentcolorants are described for example, in U.S. Pat. No. 9,828,513 (Lussieret al.), the disclosure of which is incorporated herein by reference.Other useful pigment colorant combinations are described in U.S. Pat.No. 8,455,570 (Lindstrom et al.), the disclosure of which isincorporated herein by reference.

Particle size determination for the a) one or more pigment colorants isdefined above. The a) one or more pigment colorants or a)anionically-stabilized pigment colorants have a 50% percentile particlesize of less than 150 nm, less than 100 nm, less than 70 nm, or evenless than 60 nm. In addition, that have a 95% percentile particles sizeof less than 300 nm, less than 150 nm, or even less than 110 nm.

In some embodiments, an ink set can comprise aqueous pigment-based inksin which the a) one or more pigment colorants is a cyan pigment, amagenta pigment, a yellow pigment, a black pigment, a green pigment, anorange pigment, a white pigment, a red pigment, a blue pigment, or aviolet pigment, and the total of all of the a) one or more pigmentcolorants independently in each aqueous pigment-based ink comprises atleast 0.1 weight % and up to and including 25 weight %, based on thetotal weight of each aqueous pigment-based ink. As noted above, any orall of these pigment colorants can be anionically-stabilized pigmentcolorants using any suitable stabilizing dispersant such as an anionicpolymer or other anionic material.

In many embodiments, for example, the anionically stabilized pigmentcolorant can be one or more of an anionically-stabilized cyan pigment,an anionically-stabilized yellow pigment, an anionically-stabilizedmagenta pigment, an anionically-stabilized green pigment, ananionically-stabilized orange pigment, an anionically-stabilized redpigment, an anionically-stabilized violet pigment, ananionically-stabilized blue pigment, an anionically-stabilized whitepigment, or an anionically-stabilized black pigment. A combination ofaqueous anionically-stabilized pigment-based inks can be provided aspart of an ink set according to the present invention. Upon dryinginkjet-printed images obtained using such anionically-stabilized pigmentcolorants in anionically-stabilized pigment-based inks, the total amountof the anionically-stabilized pigment colorants can be at least 40weight % and up to and including 60 weight %, based on the total weightof the inkjet-printed image.

The a) one or more pigment colorants can be present independently ineach aqueous pigment-based ink in an amount of at least 0.1 weight % orat least 1 weight %, and up to and including 8 weight %, or up to andincluding 15 weight %, or even up to and including 25 weight %, based onthe total weight of the aqueous pigment-based ink.

Useful a) one or more pigment colorants can be obtained from variouscommercial sources including but not limited to, BASF, Clariant, SunChemical, Cabot Corp., and Orion Engineered Carbons.

Each aqueous pigment-based ink, including the two or more differentaqueous pigment-based inks incorporated within an ink set, within anarticle, or used in a method according to the present invention, mustcomprise b) one or more water-miscible humectants, as defined below,that are generally water miscible organic solvents (or “co-solvents”),and consist essentially of compounds, each of which independently has acarbon atom to oxygen atom ratio of at least 1.0:1.0 or at least 1.3:1.0and up to and including 2.7:1.0. The carbon atom to oxygen atom ratiocan be the same or different for the various b) one or morewater-miscible humectants in the respective aqueous pigment-based inks.The humectants do not contain heteroatoms, such as nitrogen or sulfur,but contain only carbon, hydrogen and oxygen atoms.

More specifically, each of the b) one or more water-miscible humectantsindependently in the one or more different aqueous pigment-based inkstypically have only two hydroxy oxygens (in two hydroxy groups). Someuseful b) water-miscible humectants can have one or more oxy or etherbond oxygens. For example, each of the b) one or more water-misciblehumectants independently in the two or more different aqueouspigment-based inks are consisting essentially of the compounds selectedfrom the following group of compounds:

-   2-(2-hydroxyethoxy)ethanol and 2-[2-(2-hydroxyethoxy)ethoxy]ethanol    (“TEG”);-   dihydroxyethane (or 1,2-ethanediol);-   dihydroxypropanes, such as 1,2-dihydroxypropane (or 1,2-propanediol)    and 1,3-dihydroxypropane (or 1,3-propanediol);-   dihydroxybutanes, such as 1,2-dihydroxybutane (or 1,2-butanediol),    1,3-dihydroxybutane (or 1,3-butanediol), 2,3-dihydroxybutane (or    2,3-butanediol), 1,4-dihydroxybutane (or 1,4-butanediol),    1,3-dihydroxy-2-methylpropane, and    1-hydroxy-2-hydroxy-2-methylpropane;-   dihydroxypentanes, such as 1,2-dyhydroxy-n-pentane (or    1,2-n-pentanediol), 1,5-dihydroxy-n-pentane (or 1,5-n-pentanediol).

More particularly, the b) one or more water-miscible humectantsindependently in the two or more different aqueous pigment-based inksprovided in an ink set, or used individually or together, consistessentially of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol,1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,2-pentanediol,2,3-pentandiol, 1,3-pentanediol, 2-(2-hydroxyethoxy)ethanol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds.

The b) one or more water-miscible humectants can be presentindependently in the various aqueous pigment-based inks useful accordingto the present invention in a total amount of at least 1 weight %, of atleast 3 weight % and up to and including 10 weight %, or up to andincluding 20 weight %, all based on the total weight of the individualaqueous pigment-based ink.

Moreover, it is highly desired that common high boiling humectants ofthe art, such as 1,2,3-trihydroxypropane (glycerol) andN-methyldiethanolamine, are either entirely absent or are present atvery low amounts in all aqueous pigment-based inks used in the presentinvention. That is, 1,2,3-trihydroxypropane (glycerol), for example, ispresent in an amount of less than 3 weight %, or desirably less than 2weight %, or more desirably less than 1 weight %, or even less than 0.5weight %, based on the total weight of all b) one or more water-misciblehumectants. For optimal lamination bond strength in the flexible inkjetprinted articles, 1,2,3-trihydroxypropane, N-methyldiethanolamine, andall other high boiling temperature, low vapor pressure humectants shouldbe excluded from all aqueous pigment-based inks.

By “consisting essentially”, it is meant that each aqueous pigment inkcontains no more than 10 weight %, and particularly from 0 weight % tono more than 5 weight %, based on the total weight of the b) one or morewater-miscible humectants, of humectant compounds that do not fallwithin the scope of the present invention described above (only twohydroxy groups).

Thus, at least 90 weight % of the total weight of b) water-misciblehumectants in each aqueous pigment-based ink consists essentially of oneor more compounds, each having a carbon atom to oxygen atom ratio of atleast 1.0:1.0 and having only two hydroxyl groups. Such compounds havinga carbon atom to oxygen atom ratio (“C:O”) of at least 1.0:1.0 or atleast 1.3:1.0, but up to and including 2.7:1.0 and only two hydroxylgroups can have a range of vapor pressures and boiling pointtemperatures as pure compounds. The advantages of the present inventioncan often be furthered by the use of higher proportions of higher vaporpressure, lower boiling temperature humectants than lower vaporpressure, higher boiling temperature humectants in humectant mixtures toaid the removal of the humectants from the printed ink deposit duringthe ink drying process following ink drop placement on a substrate. Thusit is frequently desirable for the predominant humectant is such amixture to have a boiling point at 1 atmosphere of at least 190° C. butnot greater than 240° C. In a similar vein, it is frequently desirablefor the predominant humectant in such a mixture to have a vapor pressureat 1 atmosphere and 25° C. of at least 0.01 mm Hg (1.3 Pa) but not lessthan 0.001 mm Hg (0.13 Pa). Quite surprisingly, aqueous pigment-basedinks useful in the present invention comprised of higher proportions ofhigher vapor pressure, lower boiling temperature dihydroxywater-miscible humectants, such as 1,2-ethanediol or 1,2-propanediol, donot suffer losses of the humectant during continuous inkjet ink fluidrecirculation that can produce significant degrees of water evaporation,and modest humectant levels succeed at producing stable drop formationwith normal printhead maintenance cycles. In addition, flexible polymerfilm webs can be printed at high speed but still dried gently and tackfree so as to avoid distorting the web under tension, and also notexhibit back side ink transfer (“offsetting”) during roll wind-up andstorage.

Mixtures of b) one or more water-miscible humectants can be used aswould be appreciated by one skilled in the art in view of the teachingpresented herein. Some mixtures are better than others in specificaqueous pigment-based inks having specific a) one or more pigmentcolorants. It is not known why some individual or mixture of b) one ormore humectants are more desirable and solve the problems describedherein with specific a) one or more pigments, as compared to others.Routine trial and error can be used to find the optimum compounds andamounts for a given aqueous pigment-based ink. For example, it has beenobserved that when “TEG” (noted above) is used in a mixture of b) one ormore water-miscible humectants, for example in an aqueous yellowpigment-based ink, it is best if the TEG is present as a “minor” (lessthan 50 weight %) amount of the total weight of b) one or morewater-miscible humectants.

In some embodiments, an ink set can comprise an aqueous cyanpigment-based ink that comprises one or more anionically-stabilized cyanpigment colorants, and the b) one or more water-miscible humectantsconsist essentially of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol,1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-pentanediol,2.3-pentanediol, 1,3-pentanediol, 2-(2-hydroxyethoxy)ethanol,2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or a combination of two or more ofthese compounds, in a total amount of at least 4 weight % and up to andincluding 8 weight %, based on the total weight of the aqueous cyanpigment-based ink;

an aqueous magenta pigment-based ink that comprises one or moreanionically-stabilized magenta pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %, based on the totalweight of the aqueous magenta pigment-based ink;

an aqueous yellow pigment-based ink that comprises one or moreanionically-stabilized yellow pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %, based on the totalweight of the aqueous yellow pigment-based ink; and an aqueous blackpigment-based ink that comprises one or more anionically-stabilizedblack pigment colorants, and the b) one or more water-misciblehumectants consists essentially of 1,2-ethanediol, 1,2-propanediol,1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol,1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 5 weight % and up to and including 10 weight %, based on the totalweight of the aqueous black pigment-based ink.

In such aqueous magenta pigment-based inks, the b) one or morewater-miscible humectants can consist essentially of one or both of1,2-propanediol and 1,2-butanediol together with2-[2-(2-hydroxyethoxy)ethoxy]ethanol in a weight ratio of 1:1 and up toand including 8.1.

Moreover, in such aqueous black pigment-based inks, the b) one or morewater-miscible humectants can consist essentially of one or both of1,2-propanediol and 1,3-propanediol together with2-[2-(2-hydroxyethoxy)ethoxy]ethanol in a weight ratio of at least 1:1and up to and including 8:1.

The useful b) one or more water-miscible humectants can be obtained fromvarious commercial suppliers such as Dow-Dupont, Shell Chemicals, AcrosOrganics, TCI, Parchem, Alfa-Aesar, Sigma-Aldrich, Hairui, Nexeo,Univar, and Fisher Chemical.

Thus, each aqueous pigment-based ink has the a) one or more pigmentcolorants and b) one or more water-miscible humectants, as defined, asthe only essential components for achieving advantages according to thepresent invention, especially the delamination improvement describedherein. Nothing else is essential for the purpose of achieving theadvantages described above. In some embodiments, however, it may beuseful to include an c) acidic polymer, or a mixture thereof, in one ormore of the aqueous pigment-based inks, which c) acidic polymer can bechosen from anionic polyurethanes and acidic styrene-acrylic polymers.Each of the c) acidic polymer can have an acid number of at least 50, orof at least 60, and up to and including 160 or up to and including 240,and if necessary, each c) acidic polymer can be neutralized withsufficient base (such as an alkali metal hydroxide or amine) to renderit dispersible or soluble in the aqueous pigment-based ink.

Representative examples of both types of c) acidic polymers aredescribed in U.S. Pat. No. 8,430,492 (Falkner et al.), the disclosure ofwhich is incorporated herein by reference. Useful anionic polyurethanescontaining a polyether diol unit can be identified as polyetherpolyurethanes and generally can have a weight average molecular weight(M_(w)) of at least 10,000 and up to and including 30,000 or at least15,000 and up to and including 25,000. Useful water-soluble orwater-dispersible anionic polyether polyurethanes can be prepared asdescribed for example in [0045]-[0049] of U.S. Patent ApplicationPublication 2008/0207811 (Brust et al.), the disclosure of which isincorporated herein by reference. The acidic groups in the anionicpolyether polyurethanes can be at least partially and up to 100%neutralized (converted into salts) using monovalent inorganic bases suchas alkaline metal hydroxides or organic amines such asdimethylethanolamine.

Representative anionic acrylic polymers and anionic styrene-acrylicpolymers useful in the present invention are described also for examplein [0061] of U.S. Patent Application Publication 2008/207811 (notedabove). Examples of useful anionic styrene-acrylic polymers includethose commercially available under the trademark JONCRYL® (BASF).

The useful amounts of such anionic polymers are readily known in the artand can be up to and including 14 weight %, or up to and including 10weight %, all based on the total weight of the aqueous pigment-basedink. Some of these anionic polymers can be used also as dispersants forthe a) one or more pigment colorants.

Other additives optionally present in any of the aqueous pigment-basedinks include colorless fluorescent colorants (dyes or pigments) andexamples of such compounds are described in U.S. Patent ApplicationPublication 2014/231674 (Cook), the disclosure of which is incorporatedherein by reference. Still other optional additives include but are notlimited to solvo-surfactants, organic co-solvents, thickeners,conductivity-enhancing agents, drying agents, waterfastness agents,viscosity modifiers, pH buffers, antifoamants, wetting agents, modifiedpolysiloxanes surfactants, non-silicone surfactants, corrosioninhibitors, biocides, fungicides, preservatives or other antimicrobialagents, fragrances or masking fragrances, defoamers (such as SURFYNOL®DF110L, PC, MD-20, and DF-70), UV radiation absorbers, antioxidants, andlight stabilizers available under the trademarks TINUVIN® (Ciba) andIRGANOX® (Ciba), as well as other additives described in Col. 17 (lines11-36) of U.S. Pat. No. 8,455,570 (Lindstrom et al.). The useful amountsof any of these additives would be readily apparent to one skilled inthe art using routine experimentation.

In addition, any of the aqueous pigment-based inks can further compriseone or more aqueous-soluble dyes that are well known in the art, forexample as described in Col. 12 of U.S. Pat. No. 8,455,570 (notedabove).

An aqueous solvent medium is generally present in each aqueouspigment-based ink in an amount of at least 75 weight % or at least 85weight %, and generally at no more than 95 weight %, based on the totalweight of the aqueous pigment-based ink. Water is the predominantsolvent in the “aqueous solvent medium”, and water-miscible orimmiscible organic solvents (other than the water-miscible humectantsdescribed above) are either absent or present in negligible amounts. Forexample, water can comprise at least 85 weight % of the total weight ofall solvents in the aqueous solvent medium.

The pH of each aqueous pigment-based ink can be adjusted if desired toat least 7 and up to and including 12, or more likely to at least 8 andup to and including 10, or in some embodiments to at least 8 and up toand including 9.5. The pH can be achieved using any suitable base suchas a hydroxide or an organic amine in a suitable amount. Buffers can beincluded to maintain the desired pH as would be readily apparent to oneskilled in the art, according to Cols. 17-19 of U.S. Pat. No. 8,455,570(noted above).

When the aqueous pigment-based ink is to be used in hardware with nickelor nickel-plated apparatus components, a corrosion inhibitor such as thesodium salt of 2- or 5-methyl-1-H-benzotriazole can be added, and the pHcan be adjusted to at least 10 and up to and including 11. If printheadsfashioned out of silicon are used for inkjet printing, the aqueouspigment-based ink pH can be adjusted to at least 7.5 and up to andincluding 10, or at least 8 and up to and including 9.5.

In some useful embodiments, two or more different aqueous pigment-basedinks, as defined herein, can be used to provide colorful inkjet printedimages or layers. Such two or more different aqueous pigment-based inkscan be provided as part of an ink set as further defined herein.

In many continuous inkjet printing machines and system, an ink set cancomprise at least one aqueous cyan pigment-based ink, at least oneaqueous magenta pigment-based ink, at least one aqueous yellowpigment-based ink, and at least one aqueous black pigment-based ink, anyand all of which can be aqueous anionically-stabilized pigment-basedinks.

In some embodiments, an ink set according to this invention can furthercomprise a particle-free colorless inkjet composition (or aqueousparticle-free fluid), for example as described in U.S. Pat. No.8,764,161 (Cook et al.), the disclosure of which is incorporated hereinby reference. Such compositions can be known as “fluids” in the art andcan have various purposes or functions such as printhead maintenance,storage, flushing, or cleaning, or use as replenishment fluids. By“particle-free,” it is meant that such compositions do not purposelycontain particulates or pigments of any type, colorless or colored. Suchparticle-free fluids can also include any suitable biocide,anti-microbial agent, or anti-fungal agent. Water is the predominantsolvent in such particle-free colorless inkjet compositions.

The durability, gloss, and other properties of an inkjet-printed imagecan be improved by the application of a colorless polymeric overcoatcomposition, which can be considered an aqueous particle-free inkjetcomposition and can be included as a component of an ink set, orprovided separately. Examples of such colorless polymeric overcoatcompositions are provided in U.S. Pat. No. 7,219,989 (Uerz et al.). Inother to achieve high inkjet printing speeds and throughput associatedwith CIJ printing, such an overcoat composition can be applied using aCIJ printhead following in-line with one or more printheads ofdrop-forming nozzles dispensing “colored” aqueous inkjet inkcompositions. Further details about such uses are provided in Col. 17(lines 16-48) of U.S. Pat. No. 8,173,215 (Sowinski et al.).

Additional aqueous particle-free inkjet compositions (or inks) that canbe included as a component of an ink set, or provided separately,include those compositions described in U.S. Pat. No. 10,189,271(Lussier et al.) that can be inkjet printed to provide colorless orcolored coatings, the disclosure of which publication is incorporatedherein by reference. Such compositions can comprise at the least, one ormore anionic polyether polyurethanes or anionic acrylic orstyrene-acrylic polymers as described above, as well as a suitableantifoamant or defoamer to reduce foaming propensities. Such aqueousparticle-free inkjet compositions can further comprise a suitablepreservative, biocide, antifungal agent, or other antimicrobial agent.

Each component or composition present in an ink set, whether colored orcolorless, may contain various other additives (such as preservatives,fragrances or masking fragrances, defoamers, surfactants, conductivityenhancing agents, drying agents, waterfastness agents, chelating agents,thickeners, anti-kogation agents, stabilizers, and buffering agents)that would be readily apparent to one skilled in the art.

Ink-Receptive Media

As shown in FIG. 1 , a simple embodiment useful in the present inventionis ink-receptive medium 10 having water-impermeable support 100 on whichaqueous-based ink-receptive layer 110 is disposed, and water-impermeablesupport 100 and aqueous-based ink-receptive layer 110 are contiguous orin direct contact with each other. In general, water-impermeable support100 can be opaque, semi-transparent, translucent, or transparent.

Suitable substrates for such media are typically planar in nature withtwo opposing surfaces or supporting sides one or both that can be inkjetprinted to provide the same or different image. Substrates can have asingle “layer” or stratum (such as a single support) or be composed ofmultiple layers or strata composed of the same or different materials.In most instances, a substrate is composed of a predominantlywater-impermeable material, such as a plastic or polymeric material or acellulosic material that is coated or laminated with one or morewater-impermeable polymeric coatings.

Thus, useful substrate materials from which water-impermeable support100 also can be constructed include but are not limited to, glossy,semi-glossy, or matte coated lithographic offset papers that typicallycomprise a paper base (support) that has been coated with awater-impermeable material to make the substrate water-impermeable, andthat can have undergone a surface calendering treatment to provide adesired surface smoothness.

In many embodiments according to this invention, the substrate can havea hydrophobic outer surface prior to the aqueous-based ink-receptivelayer being formed thereon. This hydrophobic outer surface can besubstantially impermeable to water or to an aqueous pigment-based inkand difficult for an aqueous pigment-based ink to wet and adhere to. Theeffect of the aqueous-based ink-receptive layer in the substrate thenis, firstly to provide a wettable surface for the aqueous pigment-basedink to contact and stick to upon impingement, thereby avoiding dropletsplatter, repellency and wander, and then to spatially fix the a)pigment colorants (and any c) acidic polymers present) by complexationand coagulation with labile multivalent metal ions, which prevents imagequality artifacts such as coalescence, mottle and intercolor bleeding.

Other useful substrates include water-impermeable materials such asresin-coated offset papers, biaxially oriented films including polyesterfilms, polyethylene materials, polypropylene materials, polystyrenefilms, and polyamide films, and the metallized versions of these polymerfilms, melt-extrusion-coated papers, and laminated papers such asbiaxially oriented support laminates such as those described in Col. 6(line 50) to Col. 7 (line 2) of U.S. Pat. No. 9,067,448 (Dannhauser etal.), the disclosure of which is incorporated herein by reference.

The outer surface of a water-impermeable (hydrophobic) substrate can bemodified or treated to increase the static surface energy to at least 45dynes/cm, or at least 50 dynes/cm and up to and including 60 dynes/cm,in order to provide adequate wettability for formation of theaqueous-based ink-receptive layer. Static surface energy modificationcan be carried out using corona discharge treatment (CDT), plasmadischarge treatment, flame ionization treatment, atomic layerdeposition, or similar treatments known in the art. Such surfacetreatment can be carried out between steps of providing the substrateand depositing an aqueous composition (as described above).

FIG. 2 illustrates another embodiment that can be used in the practiceof this invention in which ink-receptive medium 20 compriseswater-impermeable support 200 and first layer 210 disposed on at leastone surface of water-impermeable support 200, which together formwater-impermeable substrate 215 for the ink-receptive medium accordingto the present invention. First layer 210 can comprise a water-based tielayer composition (described below) and can be located on at least onesurface of water-impermeable support 200 and underneath aqueous-basedink-receptive layer 220. In many embodiments, water-impermeable support200 can be composed of a water-impermeable material such as a polymericfilm, or a co-extrudate or a laminate of two more polymeric films asreferred to above in U.S. Pat. No. 9,067,448 (Cols. 6-7). Other usefulmaterials for water-impermeable support 200 are also described above.

First layer 210 can be known in the art as a “tie-layer” and it isgenerally water-based (or aqueous-based) meaning that it is providedfrom an aqueous formulation and serves to improve the adhesion ofaqueous-based ink-receptive layer 220 to water-impermeable support 200when it is composed of one or more water-impermeable materials such as apolymeric film (such as a polyester film) or a polyethylene coatedpaper. Examples of hydrophilic materials useful for composing firstlayer 210 include but are not limited to, halogenated phenols, partiallyhydrolyzed vinyl chloride-vinyl acetate copolymers, vinylidenechloride-methyl acrylate-itaconic acid terpolymers, vinylidenechloride-acrylonitrile-itaconic acid terpolymers, and glycidyl(meth)acrylate polymers. Other useful materials include any polymers,copolymers, reactive polymers and copolymers, and mixtures thereof, thatexhibit effective bonding between the topcoat layer and the substrate.Water-soluble or water-dispersible polymers can also be used includingbut not limited to, poly(vinyl alcohol)s, polyvinyl amine, poly(vinylpyrrolidone), gelatin and gelatin derivatives, cellulose ethers,poly(oxazoline), poly(vinyl acetamide), partially hydrolyzed poly(vinylacetate/polyvinyl alcohol), poly(acrylic acid), poly(acrylamide),poly(alkylene oxide)s, sulfonated or phosphonated polyesters orpolystyrenes, casein, zein, albumin, chitin, chitosan, dextran, pectin,a collagen derivative, collodion, agar-agar, arrowroot, guar,carrageenan, tragacanth, xanthan, rhamsan, and various polymericlattices. Particularly useful first layer materials include polyvinylalcohols, polyvinyl amines, gelatin and gelatin derivatives,poly(ethyleneimine), epoxy resins, polyurethanes, polyacrylamides andderivatives or copolymers thereof, and mixtures of any of thesematerials.

While first layer 210 can be a single discrete layer, it can alsocomprise two or more water-based (aqueous-based) sub-layers, each ofwhich comprises the same or different hydrophilic materials describedabove. For example, first layer 210 can be composed of a first sub-layerand a second sub-layer, wherein the first sub-layer comprisespoly(ethyleneimine) and an epoxy resin modified with an acidifiedaminoethylated vinyl polymer, and the second sub-layer that is disposedon the first sub-layer comprises a crosslinked polyvinyl alcohol.

The total dry coverage of the one or more hydrophilic materials in firstlayer 210 (or a tie-layer), whether comprised of a single discrete layeror multiple sub-layers, can be at least 0.05 g/m² and up to andincluding 12 g/m², or at least 0.05 g/m² and up to and including 1.5g/m².

Further details about first layer 210 (or tie-layer) construction andmaterials are provided in U.S. Pat. No. 9,376,582 (noted above), thedisclosure of which is incorporated herein by reference.

However, one advantage of the present invention is that such firstlayers can be omitted if desired and lamination bond strength between aninkjet-printed image of deposited aqueous pigment-based inks and aflexible polymeric film or paper (described below) is not diminished.

For the ink-receptive media useful in the present invention, theaqueous-based ink-receptive layer, upon drying, generally has a drycoating weight of at least 0.1 g/m² or at least 0.3 g/m² and up to andincluding 3 g/m², or up to and including 5 g/m² or up to and including10 g/m². Such aqueous-based ink-receptive layer comprises the components(a), (b) and optionally components (c) and (d) as described above, inthe described dry coverage amounts.

Once the aqueous composition is applied to a substrate, it can be driedto form an ink-receptive medium having an aqueous-based ink-receptivelayer, which has various uses. For example, such articles areparticularly useful in inkjet printing methods to provide a monochromeor multi-color image or layer on the aqueous-based ink-receptive layerusing one or more different aqueous pigment-based inks (as definedabove), followed by drying of all applied materials, to removesubstantially all solvent medium including water. A functional layer(described below) can be formed on the deposited a) one or more pigmentcolorants (such as anionically-stabilized pigment colorants) asdescribed in more detail below. Details of such processes for making theink-receptive media and inkjet-printed articles are also provided below.

Method for Making Ink-Receptive Media

An aqueous composition (as described above) can be used to prepare orform an aqueous-based ink-receptive layer on one or both opposing sides(or surfaces) of a substrate (as described above). Thus, a substrate,particularly a water-impermeable substrate, can be chosen and an aqueouscomposition can be disposed on at least one surface of the substrate toprovide an aqueous-based ink-receptive layer.

The method procedures and apparatus used to accomplish this can beselected from various known coating techniques, including but notlimited to spraying, rod coating, blade coating, gravure coating,(direct, reverse, or offset), flexographic coating, size press (puddleand metered) coating, extrusion hopper coating, and curtain coating,using suitable equipment known for these purposes. After drying usingsuitable drying conditions and equipment, inkjet printing can be carriedout on the resulting aqueous-based ink-receptive layer.

In some embodiments, an aqueous-based ink-receptive layer can be formed“in-line” as part of a substrate manufacturing process (such as a filmmaking process). Alternatively, the aqueous-based ink-receptive layercan be formed in a separate coating step after the manufacture of awater-impermeable substrate. Moreover, the aqueous-based ink-receptivelayer can be formed in-line as part of an inkjet printing operation(such as a CIJ printing operation), wherein the aqueous composition isapplied to a substrate in a “pre-coating” or “pre-treatment” stationprior to inkjet printing of one or more aqueous pigment-based inks. Suchpre-coating operations can be designed to provide uniform coatingcoverage, or in some instances, only a specific area of the substratecan be provided with the aqueous composition. While the applied aqueouscomposition can be dried completely before inkjet printing, completedrying may not be necessary at that time and overall drying of bothapplied aqueous-based ink-receptive layer and deposited a) one or morepigment colorants in the deposited aqueous pigment-based inks in animage can be carried out at the same time using suitable conditions andequipment that are known in the art.

If an ink-receptive medium is prepared with a first layer or multiplesub-layers, as described above, such first layer or multiple sub-layerscan be formed using techniques and equipment described above for formingan aqueous-based ink-receptive layer. For example, the first layer andaqueous-based ink-receptive layer can be separately formed on a supportto form a substrate in distinct or separate coating operations with anintermediate drying operation. Alternatively, the first layer can beformed in-line as part of an ink-receptive media manufacturing or aninkjet printing operation so that multiple layers are formed or appliedsequentially with or without drying between layer applications. Furtherdetails of such processes are provided in Cols. 7-8 of U.S. Pat. No.9,376,582 (noted above). The formation of multiple layers inink-receptive media is particularly desirable using slide-hopper andcurtain coating techniques.

Method and Apparatus for Inkjet Printing

Ink-receptive media prepared as described above can be inkjet printed bydepositing directly onto the outer surface of the aqueous-basedink-receptive layer, one or more aqueous pigment-based inks comprisinga) one or more pigment colorants and b) one or more water-misciblehumectants (as described above) to provide an inkjet-printed pattern orimage of one or more deposited aqueous pigment-based inks. Such aqueouspigment-based-inks can be aqueous anionically-stabilized pigment-basedinks. The aqueous pigment-based inks can be printed onto the resultingwater-impermeable substrates as described above, especially to provideplastic packaging materials such as laminated plastic wrap (that is,flexible inkjet-printed articles as described below) and other materialsthat would be readily apparent to one skilled in the art.

While the aqueous compositions and aqueous pigment-based inks describedherein can be useful in drop-on-demand (DOD) printing systems, theadvantages of the present invention are particularly evident when thepresent invention is carried out using continuous inkjet (CIJ) printingprocesses, equipment, and systems. There are several CIJ printingprocesses known in the art, and the present invention is not limited toa particular CIJ process, but there may be certain CIJ processes thatare more useful than others. In general, such CIJ processes use one ormore aqueous pigment-based inks that are held in individual main fluidsupplies and ejected through one or more printheads (containing nozzles)such as full-width printheads. Unprinted aqueous pigment-based ink(s)can be collected and recycled through the printing system multiple timesuntil it (they) is (are) used up. In addition, the CIJ printing systemcan have incorporated replenisher systems. Details of such CIJprocesses, equipment, and systems are provided for example in U.S. Pat.No. 8,173,215 (Sowinski et al.), U.S. Pat. No. 8,991,986 B2 (Sowinski etal.), and U.S. Pat. No. 9,010,909 B2 (Nelson et al.), the disclosures ofwhich are incorporated herein by reference.

Thus, in most CIJ inkjet printing processes, each aqueous pigment-basedink can be ejected or printed from a respective main fluid supplydedicated to a particular aqueous pigment-based ink only, as acontinuous stream that is broken into both printing drops andnon-printing drops using a drop generator of a suitable design. Thenon-printing drops of the respective continuous streams of aqueouspigment-based inks can be collected using suitable collecting means suchas a “catcher” and returned to the respective main fluid supplies. Eachof the non-printed aqueous pigment-based inks (for example, aqueousanionically-stabilized pigment-based inks) can be continuouslyrecirculated between the respective main fluid supplies and a dropgenerator as long as necessary. This entire scenario can be carried outusing a single (first) aqueous pigment-based ink alone, or incombination with one or more additional aqueous pigment-based inkshaving the same or different “colors” or hues as the first aqueouspigment-based ink. The multiple aqueous pigment-based inks can be theninkjet printed in a chosen sequence that can be controlled by softwareand digital input, in a controlled manner, to provide a multicolorinkjet printed image on the surface of the ink receiving medium. Forexample, in some CIJ printing systems, one or more different aqueouspigment-based inks can be deposited in response to electrical signalsgoverned by digital input.

The printing methods according to the present invention can be carriedout using a continuous high-speed commercial inkjet printer, for examplein which the inkjet printer forms colored images using one or moredifferent printheads such as full-width printheads with respect to theink-receptive media, in sequence, in which the different colored partsof images are to be registered. One type of continuous inkjet (CIJ)printing, commonly referred to as “continuous stream,” uses apressurized ink source that produces a continuous stream of printingdrops (droplets) from a main fluid supply for each aqueous pigment-basedink, or a continuous stream that is broken into both printing drops andnon-printing drops. Continuous inkjet printers can utilize electrostaticcharging devices as drop generators that are placed close to the pointwhere a filament of working inkjet composition breaks into individualdrops that are electrically charged and then directed to an appropriatelocation by deflection electrodes having a large potential difference.Where no color image is desired, the non-printing drops can be deflectedinto an ink-capturing mechanism and disposed of or recycled by returningthem to the original main fluid supply. When a printed color image isdesired, the printing drops are not deflected but are allowed to strikethe topcoat layer of the ink-receptive medium in designated locations.Alternatively, deflected printing droplets for each or all inks can beallowed to strike the outermost surface of the inkjet receiver mediumwhile non-deflected non-printing drops can be collected and returned tothe main fluid supply.

CIJ printing systems are generally comprised of two main equipmentcomponents, a fluid system (including one or more ink reservoirs or mainfluid supplies) and one or more printheads. Each aqueous pigment-basedink can be pumped through a supply line from its main fluid supply to amanifold that distributes the ink to a plurality of orifices ofprintheads, typically arranged in linear array(s), under sufficientpressure to cause ink streams to issue from the orifices of theprinthead(s). As noted above, stimulations can be applied to theprinthead(s) to cause those ink streams to form streams of uniformlysized and spaced drops that are deflected in a suitable manner, intoprinting or non-printing paths. This discrimination can also beaccomplished when the printhead digitally creates large and small drops.In some embodiments, small drops are deflected by an air current andreturned to the main fluid supply; and large drops, being less affectedby the air current, are printed onto the ink-receptive medium. In otherembodiments, large drops are deflected in a designed manner and smalldrops are printed.

In addition, it may be useful to apply an aqueous colorless or aqueousparticle-free ink composition or fluid to a pattern or image of one ormore deposited aqueous pigment-based inks. This operation can be carriedout simultaneously or sequentially with inkjet printing of the “colored”aqueous pigment-based ink(s). For example, according to U.S. Pat. No.10,189,271 (Lussier et al.), a colorless lacquer or ink composition canbe applied over single- or multi-color inkjet-printed image.

Useful CIJ printing processes and equipment can include replenishmentsystems that measure ink electrical resistivity and are described forexample in U.S. Pat. No. 5,526,026 (Bowers), the disclosure of which isincorporated herein by reference and in EP 0597628B1 (Loyd et al.).Useful CIJ printing processes and equipment that employ other means foraqueous pigment-based ink concentration sensing are disclosed in U.S.Pat. No. 7,221,440 (McCann et al.), the disclosure of which isincorporated herein by reference, and in EP 0571784B1 (McCann et al.)and EP 1,013,450B1 (Woolard et al.).

In some embodiments, basic ink replenishment can be carried out using afluid system containing an ink resistivity measurement cell throughwhich an aqueous pigment-based ink passes as it is being recirculatedthrough the ink handling portion of the system, including the printhead.A calculation means determines the resistance of the ink resistivitycell. A logic and control unit, responsive to the calculation means,controls the transfer of aqueous pigment-based ink from a supplemental“ink” supply and the transfer of an aqueous particle-free fluid(“carrier fluid”) from a replenishment carrier fluid supply to thesystem main fluid supply, to maintain desired resistivity in the aqueouspigment-based ink. The volume of each aqueous pigment-based ink ismonitored by a float valve position, and when a predetermined volume hasbeen depleted, the predetermined volume is replaced by either aqueouspigment-based ink from the supplemental ink supply or by carrier fluidfrom the replenishment carrier fluid supply. Thus, the first and anyadditional aqueous pigment-based inks can be replenished, respectively,with respective aqueous pigment-based inks.

In other examples, the method according to the present invention canfurther comprise replenishing a main fluid supply with an aqueousparticle-free fluid that has a dynamic viscosity of less than or equalto 5 centipoise (5 mPa-sec) at 25° C. as measured using a rolling ballviscometer.

In some embodiments, the method according to the present invention iscarried out using a CIJ printing system utilizing a plurality ofprinting drops formed from a continuous fluid stream, and non-printingdrops of a different volume than the printing drops are diverted by adrop deflection means into a “gutter” for collection and recirculation.Details about such CIJ printing systems and equipment are provided forexample in U.S. Pat. No. 6,588,888 (Jeanmaire et al.), U.S. Pat. No.6,554,410 (Jeanmaire et al.), U.S. Pat. No. 6,682,182 (Jeanmaire etal.), U.S. Pat. No. 6,793,328 (Jeanmaire et al.), U.S. Pat. No.6,866,370 (Jeanmaire et al.), U.S. Pat. No. 6,575,566 (Jeanmaire etal.), and U.S. Pat. No. 6,517,197 (Hawkins et al.), and in U.S. PatentApplication Publications 2002/0202054 (Jeanmaire et al.), thedisclosures of all of which are incorporated herein by reference.

In other embodiments, an aqueous pigment-based ink can be printed usingan apparatus capable of controlling the direction of the formed printingdrops and non-printing drops by asymmetric application of heat to thefluid stream that initializes drop breakup and serves to steer theresultant drop as described for example in U.S. Pat. No. 6,079,821(Chwalek et al.) and U.S. Pat. No. 6,505,921 (Chwalek), the disclosureof both of which are incorporated herein by reference. Useful agitation,heated supply, printhead, and fluid filtration means for CIJ printingare described for example in U.S. Pat. No. 6,817,705 (Crockett et al.),the disclosure of which is incorporated herein by reference.

A simple schematic of a useful CIJ printing system is also shown in FIG.1 of U.S. Pat. No. 8,764,161 (Cook et al.), the disclosure of which isincorporated herein by reference.

Inkjet-Printed Articles Inkjet-printed articles prepared according tothe present invention comprise a substrate particularly those composedof a water-impermeable material (as described above) in which anaqueous-based ink-receptive layer had been formed (as described above),and on which an inkjet-printed image has been formed by inkjet printing.As noted above, such inkjet-printed image can be monochrome (singlecolor) or multi-color or even colorless, or a colorless image or layercan be formed over a monochrome or multi-color inkjet-printed image. Inthe inkjet-printed image, each of the one or more a) pigment colorants(such as anionically-stabilized pigment colorants) can be present in anamount of at least 40 weight % and up to and including 60 weight %,based on the total weight of the inkjet printed image, where most of theremaining deposited weight is comprised of one or more c) acidicpolymers. Such inkjet-printed images can contain small amounts ofresidual b) one or more humectants as such compounds are generallychosen so that most of them are evaporated during drying stages ofinkjet printing.

For example, the inkjet-printed image can be formed by depositingdirectly onto the outer surface of the aqueous-based ink-receptivelayer, two or more aqueous pigment-based inks, defined as follows, toprovide an inkjet-printed image comprising two or more depositedanionically-stabilized pigment colorants,

each of the two or more aqueous pigment-based inks comprising:

a) one or more anionically-stabilized pigment colorants defined asfollows, wherein 50% of the volume of each is provided by pigmentcolorant particles having a diameter of less than 100 nm, and 95% of thevolume of each is provided by pigment colorant particles having adiameter of less than 150 nm, said particle size diameters beingmeasured using a dynamic light scattering particle sizing instrument;

b) one or more water-miscible humectants defined as follows; and

c) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink,

wherein the two or more aqueous pigment-based inks are selected from thefollowing:

an aqueous cyan pigment-based ink that comprises one or moreanionically-stabilized cyan pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %;

an aqueous magenta pigment-based ink that comprises one or moreanionically-stabilized magenta pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %;

an aqueous yellow pigment-based ink that comprises one or moreanionically-stabilized yellow pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %; and

an aqueous black pigment-based ink that comprises one or moreanionically-stabilized black pigment colorants, and the b) one or morewater-miscible humectants consists essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 5 weight % and up to and including 10 weight %,

all amounts being based on the total weight of the respective aqueouspigment-based ink.

The combination of anionically-stabilized pigment colorants in suchinkjet printed images can be, after drying, at least 40 weight % and upto and including 60 weight %, based on the total weight of theinkjet-printed image.

In some embodiments for example, as illustrated in FIG. 3 ,inkjet-printed article 30 can comprise water-impermeable substrate 300that is composed of water-impermeable support 310 and first layer 320disposed thereon; aqueous-based ink-receptive layer 330 disposed onfirst layer 320; inkjet-printed image 340 disposed on aqueous-basedink-receptive layer 330, and functional layer 350 disposed oninkjet-printed image 340, which functional layer 350 can be a whiteopacifying layer, a transparent (or clear) protective layer, or anadhesive layer comprising an adhesive that can have a protective layeradhered thereto.

For example, a white opaque layer can be present as a functional layerto provide desired opacity to the resulting inkjet-printed article,particularly when the water-impermeable substrate is transparent ortranslucent. Any known opaque, aqueous-based opacifying layercomposition can be used to form such functional layers including but notlimited to, aqueous-based white flexographic ink compositions sold asBianco Base 100 by Sun Chemical Corporation and Flint Group Water HMJ90104. Any commercially available aqueous-based latex ink can be used toprovide a white opaque layer, including for example WB MSQUARED™ DPQ-173or AQUALAM™ 18350 aqueous-based white ink from Sun Chemical Corporation,which aqueous-based white ink comprises a polyurethane latex binder.

A transparent (or clear) protective layer can be used as a functionallayer to protect the inkjet-printed article against environmental andphysical damage and stress, provide abrasion resistance, resistance tofingerprints, and delamination resistance (especially if it has multipleproperties). Such transparent protective layers and compositions used toprepare them are described in U.S. Patent Application Publication2018/0051184 (noted above). In addition, known aqueous-based overprintvarnishes such as DBP-1555 (Sun Chemical), Haut Brilliant 17-604327-7(Siegwerk) and Michael Huber Munchen 877801 Varnish Anticurling can beused.

An adhesive layer can be provided as a functional layer comprising anadhesion especially in articles used as flexible laminated packaging(for example, flexible inkjet-printed articles described below) whereinit is desired to bond a separate water-impermeable film to aninkjet-printed article. Classes of useful adhesives includeaqueous-based, solvent-less, and solvent-based adhesives. Usefulexamples of aqueous-based adhesives used in such adhesive layers includebut are not limited to, Dow Chemical ROBOND™ acrylic adhesives L90M,L148, and L330 that can be used in combination with a crosslinking agentsuch as Dow Chemical CR 9-101. Representative polyurethane aqueous-basedadhesives are AQUALAM™ polyurethane aqueous-based adhesives from DowChemical that can be used in combination with the Dow Chemical CR 7-103crosslinking agent, and POLURFLEX 8414/7019 (Sapici, Italy).

Useful examples of solvent-based adhesives used in such adhesive layersinclude but are not limited to, two component polyurethane systems fromDow Chemical (ADCOTE 577/CR 87-124 or L 719A/CR 719C) or Sapici(3714/6846).

Solvent-less adhesive are advantageous in that they are 100% solids anddo not require drying of the adhesive after application to aninkjet-printed image. Lower adhesive raw material costs and adhesivelaydowns also result in significant cost savings over solvent-based orwater-based adhesives. Useful examples of solvent-less adhesives used insuch adhesive layers include but are not limited to, two componentpolyurethane systems from Dow Chemical (MOR-FREE L75-164/C-411) orSapici (7858/6076).

Although functional layers with individual functions are describedseparately above, it is also possible to combine two or more functions(for example, opacity and adhesion) into a single functional layer. Suchcombinations are described for example in Col. 18 (lines 24-37) of U.S.Pat. No. 9,376,582 (noted above). In addition, the functional layerdescriptions here are intended to be illustrative and not limiting asother functional layers are possible as would be readily apparent to oneskilled in the art.

As shown in FIG. 3 , when functional layer 350 is aqueous-based(supplied out of an aqueous formulation), it can be applied or formedusing any of the methods described above for applying or forming firstlayer 320 and aqueous-based ink-receptive layer 330, including knowncoating and digital deposition processes. For example, functional layer350 can be applied as a flood coating across the entire surface of theinkjet-printed article, or it can be applied in a pattern-wise orimage-wise fashion using any suitable pattern-forming means such asflexographic or gravure means. If functional layer 350 is solvent-free,it can be applied using a melt extrusion process wherein the molten orviscous solventless composition is extruded as a continuous layer overthe surface of the dried aqueous-based inkjet printed image 340.Following melt-extrusion, functional layer 350 can be further processedusing heat and pressure to improve adhesion, followed by cooling. Insome embodiments, a solventless composition can be a two-part reactivecomposition intended to serve as an adhesive to which a continuoustransparent protective functional layer is laminated using heat orpressure.

In some other embodiments, the inkjet-printed article according to thepresent invention is simpler in structure (not shown) compared to thatillustrated in FIG. 3 . In such embodiments, aqueous-basedinkjet-printed image 340 is disposed directly on the aqueous-basedink-receptive layer 330. Thus, first layer 320 is omitted in suchembodiments. Functional layer 350 can be present or omitted from suchembodiments.

Other useful embodiments of ink-receptive media and resultinginkjet-printed articles, with various layer constructions, can beconceived of and prepared by a skilled artisan using the teachingprovided herein.

Flexible Inkjet-printed Articles and Method for Preparing Them

The inkjet-printed articles prepared according to the present inventionas described above, can be used to provide “flexible inkjet-printedarticles” that comprise laminated multilayer structures that tend to beflexible and desirably transparent (except for any inkjet-printedimage).

FIG. 4 illustrates one such embodiment, showing flexible inkjet-printedarticle 40 that comprises water-impermeable substrate 400 that iscomposed of water-impermeable support 410 and first layer 420 disposedthereon; aqueous-based ink-receptive layer 430 disposed on first layer420; inkjet-printed image 440 disposed on aqueous-based ink-receptivelayer 430, and functional layer 450 disposed on inkjet-printed image440, which functional layer 450 can comprise an adhesive material, orprovide other “functional” properties (such as opacity or protectivefeatures) as described above.

Laminated to functional layer 450 is flexible polymeric film or paper460 that can be comprised of one or more materials that are generallyflexible and in many instances, can be opaque, transparent, ormetallized, and can be water-impermeable as in the case ofwater-impermeable polymeric films that can be composed of a polyester,polyimide, polycarbonate, polystyrene, polyolefin such as orientedpolypropylene or polyethylene, polyurethane, polyvinyl chloride,polyvinylidene chloride, or a mixture of two or more of these materialsor a laminate of two or more layers of such materials.

Inkjet-printed article 40 can be used as flexible packaging materials ormulti-layer labels. Laminated flexible polymeric film or paper 460 canbe transparent (clear) or opaque, and can be metallized with imbeddedmetal particles or flakes or have a metal foil in its structure, such asmetallized polymeric films. It is particularly useful that functionallayer 450 be a white opaque or transparent protective layer arrangedbetween flexible polymeric film or paper 460 and inkjet-printed image440.

Useful adhesive materials in an adhesive composition to enable theformation of a flexible inkjet printed article include but are notlimited to, water-based polyurethane resins and other materialsdescribed above for the functional layer. Both solvent-based andwater-based adhesives can be used and such materials would be readilyapparent to those skilled in the flexible packaging art. Useful adhesivematerials can be opaque or clear (transparent) when dried. For example,useful solvent-based adhesives used in solvent-based laminationprocedures include but are not limited to, solvent-based polyurethaneresins. Moreover, water-based adhesives useful in water-based laminationprocedures include but are not limited to water-based polyurethaneresins. Solventless polyurethane resins can also be used.

It is desirable that flexible polymeric film or paper 460 is adhered tofunctional layer 450 to provide a lamination bond strength greater than1.0 N/cm as measured for example, an MTS SINTECH® 1/G ElectromechanicalTesting System as described in further detail below in the workingexamples.

The present invention also provides flexible inkjet-printed articlessimilar to that shown in FIG. 4 , but from which first layer 420 isomitted, so that substrate 400 consists only of water-impermeablesupport 410.

While the adhesive material can be incorporated into functional layer450, an adhesive material can be provided separately or additionally onflexible polymeric film or paper 460. In such embodiments, it is alsopossible to omit functional layer 450 or to use it for functions otherthan adhesive purposes.

As a skilled worker would appreciate from the foregoing discussion, suchflexible inkjet-printed articles can be prepared by, in order:

A) providing a suitable substrate as described above, such as awater-impermeable substrate;

A′) forming an aqueous-based ink-receptive layer thereon using anysuitable aqueous composition and means as described above;

B) depositing directly on an outer surface of the aqueous-basedink-receptive layer, one or more aqueous pigment-based inks to providean inkjet-printed image of one or more deposited aqueous pigment-basedinks, all of which are described above;

C) drying the one or more deposited aqueous pigment-based inks to removesubstantially all water (and other solvents) and low boiling b) one ormore water-miscible humectants from them (as well as from the aqueouscomposition if present) using any suitable drying means and conditionsas would be readily apparent to one skilled in the art, to form aninkjet-printed image;

D) forming a functional layer comprising an adhesive composition on theinkjet-printed image, and which functional layer can provide multiplefunctions as described above; and

E) adhering a flexible polymeric film or paper to the functional layer,to form a flexible printed article.

The present invention provides at least the following embodiments andcombinations thereof, but other combinations of features are consideredto be within the present invention as a skilled artisan would appreciatefrom the teaching of this disclosure:

1. An ink set comprising two or more aqueous pigment-based inks,

each aqueous pigment-based ink having at least 75 weight % and up to andincluding 95 weight % of water, and comprising:

a) one or more pigment colorants;

b) one or more water-miscible humectants that are present in a totalamount of at least 1 weight % and up to and including 20 weight %, andconsist essentially of compounds, each of which has a carbon atom tooxygen atom ratio of at least 1.0:1.0 and only two hydroxy groups;

and optionally,

c) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, and each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink,

wherein the weight % amounts of water and the b) water-misciblehumectants are based on the total weight of each aqueous pigment-basedink.

2. The ink set of embodiment 1, wherein the (b) one or morewater-miscible humectants consist essentially of compounds, each ofwhich has a carbon atom to oxygen atom ratio of at least 1.0:1.0 and upto and including 2.7:1.0.

3. The ink set of embodiment 1 or 2, wherein the b) water-misciblehumectants consist essentially of 1,2-ethanediol, 1,2-propanediol,1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol,1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds.

4. The ink set of any of embodiments 1 to 3, wherein the b) one or morewater-miscible humectants are present independently in the two or moredifferent aqueous pigment-based inks in a total amount of at least 3weight % and up to and including 10 weight %, based on the total weightof each aqueous pigment-based ink.

5. The ink set of any of embodiments 1 to 4, wherein the a) one or morepigment colorants is a cyan pigment, a magenta pigment, a yellowpigment, a black pigment, a green pigment, an orange pigment, a whitepigment, a red pigment, a blue pigment, or a violet pigment, and thetotal amount of a) pigment colorants independently present in each ofthe aqueous pigment-based inks is at least 0.1 weight % and up to andincluding 25 weight %, based on the total weight of each aqueouspigment-based ink.

6. The ink set of any of embodiments 1 to 5, wherein 50% of the volumeof each of the a) one or more pigment colorants is provided by pigmentcolorant particles having a diameter of less than 100 nm, and 95% of thevolume of each of the a) one or more pigment colorants is provided bypigment colorant particles having a diameter of less than 150 nm, theparticle size diameters being measured using a dynamic light scatteringparticle sizing instrument.

7. The ink set of any of embodiments 1 to 6, wherein at least one of thetwo or more aqueous pigment-based inks is an aqueous cyan pigment-basedink that comprises one or more anionically-stabilized cyan pigmentcolorants, and the b) one or more water-miscible humectants consistessentially of 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol,1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-pentanediol,2.3-pentanediol, 1,3-pentanediol, 2-(2-hydroxyethoxy)ethanol,2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or a combination of two or more ofthese compounds, in a total amount of at least 4 weight % and up to andincluding 8 weight %, based on the total weight of the aqueous cyanpigment-based ink.

8. The ink set of any of embodiments 1 to 7, wherein at least one of thetwo or more aqueous pigment-based inks is an aqueous magentapigment-based ink that comprises one or more anionically-stabilizedmagenta pigment colorants, and the b) one or more water-misciblehumectants consist essentially of 1,2-ethanediol, 1,2-propanediol,1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol,1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %, based on the totalweight of the aqueous magenta pigment-based ink.

9. The ink set of embodiment 8, wherein the b) one or morewater-miscible humectants consist essentially of one or both of1,2-propanediol and 1,2-butanediol together with2-[2-(2-hydroxyethoxy)ethoxy]ethanol in a weight ratio of 1:1 and up toand including 8:1.

10. The ink set of any of embodiments 1 to 9, wherein at least one ofthe two or more aqueous pigment-based inks is an aqueous yellowpigment-based ink that comprises one or more anionically-stabilizedyellow pigment colorants, and the b) one or more water-misciblehumectants consist essentially of 1,2-ethanediol, 1,2-propanediol,1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol,1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %, based on the totalweight of the aqueous yellow pigment-based ink.

11. The ink set of any of embodiments 1 to 10, wherein at least one ofthe two or more aqueous pigment-based inks is an aqueous blackpigment-based ink that comprises one or more anionically-stabilizedblack pigment colorants, and the b) one or more water-misciblehumectants consists essentially of 1,2-ethanediol, 1,2-propanediol,1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol,1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 5 weight % and up to and including 10 weight %, based on the totalweight of the aqueous black pigment-based ink.

12. The ink set of embodiment 11, wherein the b) one or morewater-miscible humectants consist essentially of one or both of1,2-propanediol and 1,3-propanediol together with2-[2-(2-hydroxyethoxy)ethoxy]ethanol in a weight ratio of at least 1:1and up to and including 8:1.

13. The ink set of any of embodiments 1 to 12, wherein each of the twoor more different aqueous pigment-based inks further comprises,independently, one or more of the c) acidic polymer.

14. The ink set of any of embodiments 1 to 13, wherein at least one ofthe two or more different aqueous pigment-based inks comprises at leastone of the a) one or more pigment colorants that isanionically-stabilized.

15. The ink set of any of embodiments 1 to 14, wherein each of the twoor more different aqueous pigment-based inks comprises at least one ofthe a) one or more pigment colorants that is anionically-stabilized.

16. The ink set of any of embodiments 1 to 15, wherein each of the a)one or more pigment colorants in all of the two or more differentaqueous pigment-based inks are anionically-stabilized.

17. The ink set of any of embodiments 1 to 16, wherein the two or moredifferent aqueous pigment-based inks independently have a dynamicviscosity of less than or equal to 5 centipoise (5 mPa-sec) as measuredat 25° C.

18. The ink set of any of embodiments 1 to 17, comprising two or moredifferent aqueous pigment-based inks, each aqueous pigment-based inkhaving at least 75 weight % and up to and including 90 weight % ofwater, and comprising:

a) one or more pigment colorants, wherein 50% of the volume of each ofthe a) one or more pigment colorants is provided by pigment colorantparticles having a diameter of less than 100 nm, and 95% of the volumeof each of the a) one or more pigment colorants is provided by pigmentcolorant particles having a diameter of less than 150 nm, the particlesize diameters being measured using a dynamic light scattering particlesizing instrument;

b) one or more water-miscible humectants defined as follows for eachindividual aqueous pigment-based ink; and

c) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink; wherein the two or more different aqueouspigment-based inks are selected from the following:

an aqueous cyan pigment-based ink that comprises one or moreanionically-stabilized cyan pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %;

an aqueous magenta pigment-based ink that comprises one or moreanionically-stabilized magenta pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 4 weight % and up to and including 8 weight %;

an aqueous yellow pigment-based ink that comprises one or moreanionically-stabilized yellow pigment colorants, and the b) one or morewater-miscible humectants consist essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol,ethylene glycol, diethylene glycol, or a combination of two or more ofthese compounds, in a total amount of at least 4 weight % and up to andincluding 8 weight %; and

an aqueous black pigment-based ink that comprises one or moreanionically-stabilized black pigment colorants, and the b) one or morewater-miscible humectants consists essentially of 1,2-ethanediol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,2,3-butanediol, 1,2-pentanediol, 2.3-pentanediol, 1,3-pentanediol,2-(2-hydroxyethoxy)ethanol, 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, or acombination of two or more of these compounds, in a total amount of atleast 5 weight % and up to and including 10 weight %,

all amounts being based on the total weight of the respective aqueouspigment-based ink.

19. The ink set of embodiment 18, comprising at least one aqueous cyanpigment-based ink, at least one aqueous magenta pigment-based ink, atleast one aqueous yellow pigment-based ink, and at least one aqueousblack pigment-based ink.

20. The ink set of embodiment 19, wherein all of the a) pigmentcolorants in each of the two or more different aqueous pigment-basedinks are anionically-stabilized.

21. A method for inkjet printing, comprising, in order:

A′) providing an ink receptive medium comprising a substrate and anaqueous-based ink-receptive layer disposed thereon, which aqueous-basedink-receptive layer has an outer surface, and comprises:

(a) one or more water-soluble salts of a multivalent metal cation in anamount of at least 0.6 weight % and up to and including 49 weight %;

(b) one or both of a polyvinyl alcohol and a polyvinyl amine, or acopolymer derived from a vinyl alcohol and a vinyl amine, in a totalamount of at least 0.5 weight % and up to and including 30 weight %;

optionally, (c) a crosslinking agent in an amount of at least 0.01weight % and up to and including 5 weight %; and

optionally, (d) silica particles in an amount of up to and including 30weight %,

all amounts (a), (b), (c), and (d) being based on the total weight ofthe aqueous-based ink-receptive layer; and

B) depositing directly onto the outer surface of the aqueous-basedink-receptive layer, one or more aqueous pigment-based inks according tothose provided in the ink set of any of embodiments 1 to 20, to providean image of one or more deposited anionically-stabilized pigmentcolorants,

each aqueous pigment-based ink having at least 75 weight % and up to andincluding 95 weight % of water, and comprising:

a) one or more anionically-stabilized pigment colorants;

b) one or more water-miscible humectants that are present in a totalamount of at least 1 weight % and up to and including 20 weight %, andconsist essentially of compounds, each of which has a carbon atom tooxygen atom ratio of at least 1.0:1.0 and only two hydroxy groups; and

optionally,

c) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, and each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink,

wherein the weight % amounts of water and of the b) water-misciblehumectants are based on the total weight of each aqueous pigment-basedink.

22. The method of embodiment 21, further comprising:

D) forming a functional layer on the image of one or more depositedanionically-stabilized pigment colorants.

23. The method of embodiment 21 or 22, wherein the (a) one or morewater-soluble salts of a multivalent metal cation comprises a cationthat is magnesium (+2), calcium (+2), barium (+2), zinc (+2), oraluminum (+3).

24. The method of any of embodiments 21 to 23, wherein the weight ratioof the (a) one or more water-soluble salts of a multivalent metal cationto the (b) one or more of a polyvinyl alcohol and a polyvinyl amine, orto the copolymer derived from a vinyl alcohol and a vinyl amine, is from0.02:1 to and including 100:1.

25. The method of any of embodiments 21 to 24, wherein both a polyvinylalcohol and a polyvinyl amine are present in the aqueous-basedink-receptive layer, in weight ratio of polyvinyl alcohol to thepolyvinyl amine is from 0.1:1 to and including 20:1, or the copolymerderived from a vinyl alcohol and a vinyl amine is present.

26. The method of any of embodiments 21 to 25, wherein the (c)crosslinking agent is present for crosslinking the polyvinyl alcohol,the polyvinyl amine, or both, or for crosslinking the copolymer derivedfrom a vinyl alcohol and a vinyl amine.

27. The method of any of embodiments 21 to 26, wherein the (d) silicaparticles are present.

28. The method of any of embodiments 21 to 27, wherein the substrate isa water-impermeable substrate that is composed of a water-impermeablematerial.

29. The method of any of embodiment 28, wherein the ink receptive mediumfurther comprises a first layer on at least one surface of thewater-impermeable substrate, and the aqueous-based ink-receptive layeris disposed on the first layer.

30. The method of any of embodiments 21 to 29, further comprisingapplying an aqueous colorless ink composition to the image of one ormore deposited aqueous pigment-based inks.

31. The method of any of embodiments 21 to 30, comprising depositing theone or more different aqueous pigment-based inks in response toelectrical signals.

32. The method of any of embodiments 21 to 31, wherein each of the oneor more different aqueous pigment-based inks is supplied from respectivemain fluid supplies as continuous streams, each of which continuousstream is broken into both printing drops and non-printing drops using adrop generator, and the method further comprising collecting andreturning the non-printing drops from the respective continuous streamsto the respective main fluid supplies, such that the non-printing dropsare continuously recirculated between the respectively main fluid supplyand the drop generator.

33. The method of any of embodiments 21 to 32, wherein the dry coverageof the aqueous-based ink-receptive layer on the substrate is at least0.3 g/m² and up to and including 3 g/m².

34. The method of any of embodiments 21 to 33 that is carried out usinga continuous inkjet printing system.

35. The method of any of embodiments of 21 to 34, comprising, in order:

A) providing a substrate;

A′) depositing an aqueous-based ink-receptive layer composition on anouter surface of the substrate to form the aqueous-based ink-receptivelayer on the outer surface of the substrate, thereby forming an inkreceptive medium;

B) depositing directly on the outer surface of the aqueous-basedink-receptive layer, the one or more aqueous pigment-based inks toprovide an image of one or more deposited anionically-stabilized pigmentcolorants;

and optionally,

D) forming a functional layer on the one or more depositedanionically-stabilized pigment colorants.

36. The method of embodiment 27, further comprising between steps A) andA′):

surface treating the substrate to increase its surface energy to atleast 45 dyne/cm.

37. The method of any of embodiments 22 to 36, wherein the formedfunctional layer is a white opacifying layer.

38. The method of any of embodiments 22 to 37, wherein the formedfunctional layer is a transparent protective layer.

39. The method of any of embodiments 22 to 38, wherein the formedfunctional layer comprises an adhesive material.

40. The method of any of embodiments 21 to 39, wherein thewater-impermeable substrate comprises a polymeric film.

41. The method of any of embodiments 21 to 40, wherein the aqueous-basedink-receptive layer is present on the water-impermeable substrate at adry coverage of at least 0.5 g/m² and up to and including 2 g/m².

42. An ink inkjet-printed article provided by the method of any ofembodiments 21 to 41.

43. A method for making a flexible inkjet-printed article, the methodcomprising, carrying out A), A′), and B) in the method of any ofembodiments 21 to 41:

C) drying the one or more aqueous pigment-based inks to removesubstantially all water to form an inkjet-printed image;

D) forming a functional layer comprising an adhesive composition on theinkjet-printed image; and

E) adhering a flexible polymeric film or paper to the functional layer,to form a flexible inkjet printed article.

44. The method of embodiment 43, wherein the adhesive compositioncomprises a water-based polyurethane resin.

45. The method of embodiment 43, wherein the adhesive compositioncomprises a solvent-based polyurethane resin.

46. The method of embodiment 43, wherein the adhesive compositioncomprises a solventless polyurethane resin.

47. The method of any of embodiments 43 to 46, wherein the adhesivecomposition is provided on the flexible polymeric film or paper.

48. The method of claim 1, wherein the flexible polymeric film is awater-impermeable film composed of a polyester, polyimide,polycarbonate, polystyrene, polyolefin, polyurethane, polyvinylchloride, polyvinylidene chloride, or a mixture of two or more of thesematerials.

49. The method of any of embodiments 43 to 48, wherein the flexiblepolymeric film or paper is adhered to the functional layer with alamination bond strength greater than 1.0 N/cm.

50. The method of any of embodiments 43 to 49, wherein the adhesivecomposition is a white opaque adhesive.

51. The method of any of embodiments 43 to 50, wherein the flexiblepolymeric film is an opaque, transparent, or metallized flexiblepolymeric film.

52. A flexible inkjet printed article prepared by a method according toany of embodiments 43 to 51, comprising:

I. the ink receptive medium;

II. the inkjet-printed image disposed on the outer surface of theink-receptive layer;

III. the functional layer comprising an adhesive composition disposed onthe inkjet-printed image; and

IV. the flexible polymeric film or paper adhered to the functionallayer.

The following Examples are provided to illustrate the practice of thisinvention and are not meant to be limiting in any manner.

The suffix (C) designates control or comparative aqueous pigment-basedinks, while the suffix (E) indicates inventive aqueous pigment-basedinks.

Preparation of Aqueous Pigment-based Inks

Polymeric Dispersant and Additive Preparation:

Polymeric Dispersant P-1

In a representative procedure, a 5-liter, three-necked, round bottomflask equipped with a mechanical stirrer, a reflux condenser, and a gasinlet was charged with 225 g of 1-methoxy-2-propanol and was spargedwith nitrogen. Akzo-Nobel Chemicals, Inc., initiator PERKADOX® AMBN-GR(1.9 g) was added with stirring. A reactant reservoir was charged with225 g of 1-methoxy-2-propanol, 23.4 g of 1-dodecanethiol, 203.5 g ofbenzyl methacrylate, 165.0 g of stearyl methacrylate, and 181.5 g ofmethacrylic acid, and the solution was degassed by nitrogen sparging.PERKADOX® AMBN-GR (7.7 g) was added and mixed in. The reactortemperature was raised to 77° C. and the reactants were pumped from thereservoir at a about 2.3 ml/min over a 360-minute period. The reactionmixture was then stirred for at least 12 hours at about 77° C. Theresulting polymer was neutralized to completion withN,N-dimethylethanolamine and stirred for 45 minutes. The resultingreaction mixture was diluted with 2,580 g of water and filtered througha Pall Corp. UILTIPLEAT® polypropylene cartridge filter. The finalpolymer solution of Polymeric Dispersant P-1 had a concentration ofabout 20 weight % solids and its pH was 8.6. The resulting acidicpolymer weight-average molecular weight (M_(w)) was 9,070 Daltons.

Polymeric Dispersant P-2

Polymeric dispersant P-2 was prepared in a similar fashion to P-1,except that 90% of the acid was reacted with potassium hydroxide duringthe neutralization step instead of with one equivalent ofN,N-dimethylethanolamine. The final polymer solution of PolymericDispersant P-2 had a concentration of about 17 weight % solids.

Polymeric Additive P-3

A benzyl methacrylate-methacrylic acid copolymer having monomer weightratio 77:23 and acid number of about 137, prepared using known methods,was 90%-neutralized with potassium hydroxide to provide an aqueoussolution. The final polymer solution of Polymeric Additive P-3 had aconcentration of about 25 weight % solids.

Polymeric Additive P-4

BASF Dispersions & Pigments North America JONCRYL® HPD 696, which is astyrene acrylic copolymer having a weight-average molecular weight(M_(w)) of 16,000 Daltons, was 90%-neutralized with potassium hydroxideto provide an aqueous solution. The final polymer solution of PolymericAdditive P-4 had a concentration of about 20 weight % solids.

Polymeric Additive P-5

In a 50-liter, round bottom flask equipped with thermometer, stirrer,water condenser, nitrogen inlet, and a vacuum outlet were placed 1,454.4g of TERATHANE® 2000 polyether glycol, 670.5 g of 2,2-bis(hydroxymethyl)propionic acid, 313.2 g of 1,4-butanediol, and 3,771 g of ethyl acetate.The temperature was adjusted to 65° C., and when a homogeneous solutionwas obtained, 1,840.9 g of isophorone diisocyanate was added, followedby 184 g of ethyl acetate. The temperature was raised to 78° C. andmaintained for 22 hours to complete the reaction. The reaction mixturewas then diluted with 86 g of 2-propanol before being neutralized with467.9 g of N,N-dimethylethanolamine. Under high shear, 18 kg ofdistilled water was added and the organic solvents were subsequentlyremoved by distillation under vacuum. The resultant aqueous dispersionwas filtered and was determined to have a non-volatile solidsconcentration of about 25 weight % and a pH value of about 8.0. Theweight-average molecular weight (M_(w)) of the resulting polyurethanedispersion was found by size exclusion chromatography to be about19,800.

Polymeric Additive P-6

JONCRYL® 586 acrylic resin (BASF) having M_(w) of about 4,300 Daltonsand acid number of about 110 was 100%-neutralized withN,N-dimethylaminoethanol to provide an aqueous solution. The finalpolymer solution of Polymeric Additive P-6 had a concentration of about20 weight % solids.

Pigment Dispersion Preparations:

Pigment Dispersion KD-1 (black pigment dispersion)

To a 2.5-gallon (9.46 liter), 9-inch (22.9 cm) diameter and 12-inch(30.5 cm) deep, double-walled stainless-steel mixing vessel containingfour baffles were added water (1,000 g) and a solution of PolymericDispersant P-1 (1,000 g of a 19.9 weight % solution). A nominal 4-inch(10.2 cm), ring-style disperser impeller (Hockmeyer Equipment Corp.D-Blade) driven by a Charles Ross & Son Co. Model HSM-100LH-2 High ShearMixer was centered 2 inches (5.1 cm) above the bottom of the mixingvessel and stirring was initiated. Cabot Corp. BLACK PEARLS® 900 carbonblack pigment colorant (500 g) was slowly integrated into the fluid.Milling media comprising beads of polystyrene resin (a copolymer derivedfrom styrene and a divinyl benzene/ethylvinyl benzene mixture) with anaverage particle diameter of 50 μm (3,000 g) was added slowly whileincreasing impeller speed. The mixture was milled with an impeller bladetip speed of about 19 m/sec for about 20 hours at an internaltemperature of 25-35° C. Samples were periodically removed, diluted, andfiltered for particle size determination by a Microtrac, Inc., NANOTRAC®NPA 150 dynamic light scattering particle size analyzer. When millingwas complete, the dispersion/media milling mixture was further dilutedwith a solution of water (1,667 g) to a final pigment concentration ofabout 12 weight %, a polymeric dispersant concentration of about 4.8weight % including the counterion, and a theoretical dispersion batchsize of about 4,167 g. The impeller was removed, and the milling mediawas separated from the dispersion by filtration. A final filtrationthrough a 0.3-μm removal efficiency Pall Corp. PROFILE II® depth filtergave roughly 4 kg of dispersion, approximately 80% yield. Thevolume-weighted 50^(th) percentile particle size was about 55 nm, andthe 95^(th) percentile particle size was about 99 nm as characterized bythe NANOTRAC® NPA 150 dynamic light scattering particle sizinginstrument.

Pigment Dispersion MD-1 (Magenta Pigment Dispersion)

Magenta pigment dispersion MD-1 was prepared in a similar manner toPigment Dispersion KD-1, except that BASF Dispersions & Pigments NorthAmerica CINQUASIA® Magenta D 4500 J was used as pigment colorant inplace of the carbon black pigment. The resulting dispersion hadapproximately 12 weight % of pigment colorant and 6.1 weight % ofpolymeric dispersant, including the counterion. The 50^(th) percentileparticle size was about 16 nm and the 95^(th) percentile particle sizewas about 59 nm as characterized by the NANOTRAC® NPA 150 dynamic lightscattering particle sizing instrument.

Pigment Dispersion CD-1 (Cyan Pigment Dispersion)

Cyan pigment dispersion CD-1 was prepared in a similar manner to PigmentDispersion KD-1, except that Pigment Blue 15:4 and Pigment Green 7 wereused as pigment colorants in a weight ratio of 3.75:1 in place of carbonblack pigment colorant and Polymeric Dispersant P-2 was used in place ofPolymeric Dispersant P-1 in the presence of Lubrizol Corp. SOLSPERSE®12000 and Polymeric Additive P-3. The resulting dispersion hadapproximately 12 weight % of pigment colorant and 8.5 weight % polymerdispersant, including the counterion. The 50^(th) percentile particlesize was about 28 nm, and the 95^(th) percentile particle size was about86 nm as characterized by the NANOTRAC® NPA 150 dynamic light scatteringparticle sizing instrument.

Pigment Dispersion YD-1 (Yellow Pigment Dispersion)

To a 10-gallon (37.85 liter), 13-inch (33 cm) diameter and 17-inch (43.2cm) deep, double-walled stainless-steel mixing vessel containing fourbaffles were added 2,560 g water and 2,400 g of a 15% solution ofPolymeric Dispersant P-2. A nominal 6-inch (15.2 cm) ring-styledisperser impeller (Hockmeyer Equipment Corp. D-Blade) driven by aHockmeyer Model HBI-7.5-11-99 High Shear Mixer was centered 3 inches(7.6 cm) above the bottom of the mixing vessel and stirring wasinitiated. Sun Chemical Co. Pigment Yellow 74 (1,200 g) was slowly addedas the pigment colorant to the fluid. Milling media comprising polymericbeads derived from styrene and a divinyl benzene/ethylvinyl benzenemixture with an average particle diameter of 50 μm (7,200 g) were addedslowly while increasing impeller speed. The mixture was milled with animpeller blade tip speed of about 20 meters/second for about 20 hours atan internal temperature of 25-30° C. The dispersion/media mixture wasfurther diluted with water (6,000 g) to a final pigment concentration ofabout 12 weight % and a Polymeric Additive P-2 concentration of about4.1 weight %. The impeller was removed, and the dispersion was separatedfrom the milling media by filtration. A final filtration through a 0.3μm particle removal rating Pall Corp. PROFILE II® depth filter yieldedroughly 10.6 kg of dispersion. The 50^(th) percentile particle size inthe dispersion was about 11 nm, and the 95^(th) percentile particle sizewas about 16 nm as determined by a NANOTRAC® NPA 150 dynamic lightscattering particle sizing instrument.

Preparation of Continuous Inkjet Ink Compositions:

Aqueous Black Pigment-Based Ink

Black aqueous pigment-based inks useful in CU inkjet printing processes,Inks K-A through K-D, were prepared using Pigment Dispersion KD-1 bycombining the components at the relative proportions reported in thefollowing TABLE I. In a representative procedure, 2.0 kg of each aqueouspigment-based ink was prepared by adding the components individually toa 2-liter high density polyethylene beaker using a 2-inch (5.1 cm)overhead impeller or a 1-inch (2.54 cm) magnetic stirrer bar rotating atabout 500 rpm to provide good mixing. The ingredients (if so indicated)were added in the following functional component order: water, acid oracid solution, amine-acid salt solution, humectant and organicco-solvent, amine base, metal corrosion inhibitor, preservative orbiocide, solvo-surfactant, soluble azo dye, pigment dispersion,surfactant, and antifoamant. Each aqueous pigment-based ink was mixedfor about 2 minutes between ingredient additions, and then it wasstirred for 1 hour after the final addition of the surfactant orantifoamant. Each aqueous pigment-based ink was filtered through a1-inch (2.54 cm) Pall Corp. 0.45 μm effective pore size ULTIPOR® N66cartridge filter at a rate of about 0.2-0.5 liter/min/inch of media. Theresulting aqueous black pigment-based inks exhibited physical propertiesthat are reported below in TABLE II.

TABLE I Functional Ink K-A (E) Ink K-B (E) Ink K-C (C) Ink K-D (C)Component Component (weight %) (weight %) (weight %) (weight %) VehicleWater 52.8 52.8 52.8 42.4 Pigment KD-1 33.8 33.8 33.8 33.8 DispersionAmine Salt Salt of N-methyl- 0.0 0.0 0.0 2.5 diethanolamine and aceticacid (15 w/w % acetic acid) Base N-Methyl- 0.0 0.0 0.0 0.74diethanolamine Binder P-5 6.0 6.0 6.0 7.2 Polymer Dispersion Binder P-60.0 0.0 0.0 4.5 Polymer Solution Humectant 1,2-Propanediol 7.0 0.0 0.00.0 Humectant 1,2-Ethanediol 0.0 7.0 0.0 0.0 Humectant1,2,3-Propanetriol 0.0 0.0 7.0 8.5 Metal COBRATEC ® 0.10 0.10 0.10 0.10Corrosion TT-50S Inhibitor (PMC Specialties Group, Inc.) PreservativePROXEL GXL ® 0.10 0.10 0.10 0.10 (Lonza, Inc.) Surfactant SURFYNOL ® 4400.18 0.18 0.18 0.18 (Evonik Corp.)

TABLE II Ink K-A Ink K-B Ink K-C Ink K-D Properties (E) (E) (C) (C)Particle Size 56 56 56 51 50^(th) percentile (nm) Particle Size 98 99102 84 95^(th) percentile (nm) pH 8.7 8.6 8.7 8.8 Conductivity (mS/cm)1.31 1.40 1.39 4.2 Density, 25° C. (g/cm³) 1.028 1.032 1.040 1.048Dynamic Viscosity, at 1.68 1.58 1.60 1.94 25° C. in mPa-sec StaticSurface Tension, 39.3 39.6 39.6 38.3 at 25° C. in mN/mAqueous Cyan Pigment-Based Inks

Aqueous cyan pigment-based inks useful for CIJ inkjet printingprocesses, Inks C-A through C-C, were prepared from the pigmentdispersion CD-1 by combining the components at the relative proportionsshown below in TABLE III in a manner analogous to that described for theaqueous black pigment-based ink K-A. These aqueous cyan pigment-basedinks exhibited physical properties that are reported below in TABLE IV.

TABLE III Functional Ink C-A (E) Ink C-B (E) Ink C-C (C) ComponentIngredient (weight %) (weight %) (weight %) Vehicle Water 74.4 72.4 72.3Pigment CD-I 16.7 16.7 16.7 Dispersion Amine Salt Salt of N-methyl- 0.00.0 1.8 diethanolamine and acetic acid (15 w/w % acetic acid) BaseN-Methyl- 0.0 0.0 0.3 diethanolamine Binder Polymer P-5 4.0 4.0 4.0Dispersion Stabilizer SOKALAN ® 0.5 0.5 0.5 Polymer K 17 P PVP Polymer(BASF) Humectant 1,2-Propanediol 4.0 6.0 0.0 Humectant1,2,3-Propanetriol 0.0 0.0 4.0 Metal Corrosion COBRATEC ® 0.1 0.1 0.1Inhibitor TT-50S (PMC Specialties Group, Inc.) Preservative PROXEL GXL ®0.1 0.1 0.1 (Lonza, Inc.) Surfactant SURFYNOL ® 440 0.1 0.1 0.1 (EvonikCorp.) Antifoamant SURFYNOL ® 0.1 0.1 0.1 DF-110L (Evonik Corp.)

TABLE IV Ink C-A Ink C-B Ink C-C Properties (E) (E) (C) Particle Size 3333 31 50^(th) percentile (nm) Particle Size 90 90 70 95^(th) percentile(nm) pH 8.5 8.5 8.5 Conductivity (mS/cm) 1.92 1.86 4.69 Density, 25° C.(g/cm³) 1.016 1.018 1.024 Dynamic Viscosity, at 1.48 1.50 1.30 25° C. inmPa-sec Static Surface Tension, 37.8 37.8 37.1 at 25° C. in mN/mAqueous Magenta Pigment-Based Inks

Aqueous magenta pigment-based inks useful for CIJ inkjet printingprocesses, Inks M-A through M-H, were prepared from Pigment DispersionMD-1 by combining the components at the relative proportions reportedbelow in TABLE V in a manner analogous to that described for the aqueousblack pigment-based ink K-A. These aqueous magenta pigment-based inksexhibited physical properties that are reported below in TABLE VI.

TABLE V Functional Ink M-A (E) Ink M-B (E) Ink M-C (E) Ink M-D (E)Component Component (weight %) (weight %) (weight %) (weight %) VehicleWater 55.3 55.8 55.8 55.8 Pigment MD-1 31.7 31.7 31.7 31.7 DispersionBinder P-5 6.0 6.0 6.0 6.0 Polymer Dispersion Humectant 1,2-Propanediol6.5 0.0 0.0 0.0 Humectant 1,2-Butanediol 0.0 6.0 0.0 0.0 Humectant1,3-Butanediol 0.0 0.0 6.0 0.0 Humectant 2-(2-Hydroxyeth- 0.0 0.0 0.06.0 oxy)ethanol Humectant 2-[2-(2- 0.0 0.0 0.0 0.0 Hydroxyethoxy)ethoxy]ethanol Humectant 1,2,3-Propanetriol 0.0 0.0 0.0 0.0 MetalCOBRATEC ® 0.1 0.1 0.1 0.1 Corrosion TT-50S Inhibitor (PMC SpecialtiesGroup, Inc.) Preservative PROXEL GXL ® 0.1 0.1 0.1 0.1 (Lonza, Inc.)Surfactant SURFYNOL ® 440 0.22 0.22 0.22 0.22 (Evonik Corp.) AntifoamantSURFYNOL ® 0.10 0.10 0.10 0.10 DF-110L (Evonik Corp.) Functional Ink M-E(E) Ink M-F (E) Ink M-G (E) Ink M-H (C) Component Component (weight %)(weight %) (weight %) (weight %) Vehicle Water 55.8 55.0 55.8 55.3Pigment MD-1 31.7 31.7 31.7 31.7 Dispersion Binder P-5 6.0 6.0 6.0 6.0Polymer Dispersion Humectant 1,2-Propanediol 0.0 0.0 3.0 0.0 Humectant1,2-Butanediol 0.0 6.0 0.0 0.0 Humectant 1,3-Butanediol 0.0 0.0 0.0 0.0Humectant 2-(2-Hydroxyeth- 0.0 0.0 0.0 0.0 oxy)ethanol Humectant2-[2-(2- 6.0 0.8 3.0 0.0 Hydroxyethoxy) ethoxy]ethanol Humectant1,2,3-Propanetriol 0.0 0.0 0.0 6.5 Metal COBRATEC ® 0.1 0.1 0.1 0.1Corrosion TT-50S Inhibitor (PMC Specialties Group, Inc.) PreservativePROXEL GXL ® 0.1 0.1 0.1 0.1 (Lonza, Inc.) Surfactant SURFYNOL ® 4400.22 0.22 0.22 0.22 (Evonik Corp.) Antifoamant SURFYNOL ® 0.10 0.10 0.100.10 DF-110L (Evonik Corp.)

TABLE VI Ink M-A Ink M-B Ink M-C Ink M-D Properties (E) (E) (E) (E)Particle Size 14 14 14 15 50^(th) percentile (nm) Particle Size 60 60 6057 95^(th) percentile (nm) pH 8.6 8.5 8.7 8.6 Conductivity (mS/cm) 1.471.61 1.53 1.60 Density, 25° C. (g/cm³) 1.023 1.021 1.018 1.026 DynamicViscosity, at 1.77 1.75 1.76 1.63 25° C. in mPa-sec Static SurfaceTension, 40.7 — — 40.7 at 25° C. in mN/m Particle Size 14 14 14 1950^(th) percentile (nm) Particle Size 60 60 60 59 95^(th) percentile(nm) pH 8.6 8.8 8.6 8.4 Conductivity (mS/cm) 1.60 1.57 1.55 1.60Density, 25° C. (g/cm³) 1.027 1.023 1.024 1.033 Dynamic Viscosity, at1.64 1.75 1.72 1.71 25° C. in mPa-sec Static Surface Tension, — 37.539.0 38.8 at 25° C. in mN/mAqueous Yellow Pigment-based Inks

Aqueous yellow pigment-based inks useful for CIJ inkjet printingprocesses, Inks Y-A through Y-H, were prepared from Pigment DispersionYD-1 by combining the components at the relative proportions reportedbelow in TABLE VII in a manner analogous to that described for theaqueous pigment-based ink K-A. These aqueous pigment-based inksexhibited physical properties that are reported below in TABLE VIII.

TABLE VII Functional Ink Y-A (E) Ink Y-B (E) Ink Y-C (E) Ink Y-D (E)Component Component (weight %) (weight %) (weight %) (weight %) VehicleWater 62.1 61.1 61.1 61.1 Pigment YD-1 25.0 25.0 25.0 25.0 DispersionBinder Polymer P-4 3.3 3.3 3.3 3.3 Solution Binder Polymer P-5 4.0 4.04.0 4.0 Solution Humectant 2-[2-(2- 5.0 0.0 0.0 0.0 Hydroxyeth-oxy)ethoxy]- ethanol Humectant 1,2-Propanediol 0.0 6.0 0.0 0.0 Humectant1,2-Butanediol 0.0 0.0 6.0 0.0 Humectant 1,2-Pentanediol 0.0 0.0 0.0 6.0Humectant 1,5-Pentanediol 0.0 0.0 0.0 0.0 Humectant 1,2,3-Propanetriol0.0 0.0 0.0 0.0 Metal COBRATEC ® 0.1 0.1 0.1 0.1 Corrosion TT-50SInhibitor (PMC Specialties Group, Inc.) Preservative PROXEL GLX ® 0.180.18 0.18 0.18 (Lonza, Inc.) Preservative KORDEK MLX ® 0.05 0.05 0.050.05 (DuPont, LLC) Surfactant SURFYNOL ® 440 0.20 0.20 0.20 0.20 (EvonikCorp.) Antifoamant SURFYNOL ® 0.08 0.08 0.08 0.08 DF-110L (Evonik Corp.)Vehicle Water 61.1 62.1 62.1 62.1 Pigment YD-1 25.0 25.0 25.0 25.0Dispersion Binder Polymer P-4 3.3 3.3 3.3 3.3 Solution Binder PolymerP-5 4.0 4.0 4.0 4.0 Solution Humectant 2-[2-(2- 0.0 0.0 1.0 1.0Hydroxyeth- oxy)ethoxy]- ethanol Humectant 1,2-Propanediol 0.0 0.0 5.00.0 Humectant 1,2-Butanediol 0.0 0.0 0.0 5.0 Humectant 1,2-Pentanediol0.0 0.0 0.0 0.0 Humectant 1,5-Pentanediol 6.0 0.0 0.0 0.0 Humectant1,2,3-Propanetriol 0.0 5.0 0.0 0.0 Metal COBRATEC ® 0.1 0.1 0.1 0.1Corrosion TT-50S Inhibitor (PMC Specialties Group, Inc.) PreservativePROXEL GLX ® 0.18 0.18 0.18 0.18 (Lonza, Inc.) Preservative KORDEK MLX ®0.05 0.05 0.05 0.05 (DuPont, LLC) Surfactant SURFYNOL ® 440 0.20 0.200.20 0.20 (Evonik Corp.) Antifoamant SURFYNOL ® 0.08 0.08 0.08 0.08DF-110L (Evonik Corp.)

TABLE VIII Ink Y-A Ink Y-B Ink Y-C Ink Y-D Properties (E) (E) (E) (E)Particle Size 14 11 11 11 50^(th) percentile (nm) Particle Size 29 16 1718 95^(th) percentile (nm) pH 8.4 8.5 8.5 8.4 Conductivity (mS/cm) 2.072.24 2.23 2.23 Density, 25° C. (g/cm³) 1.021 1.018 1.017 1.015 DynamicViscosity, at 1.58 1.54 1.59 1.62 25° C. in mPa-sec Static SurfaceTension, 36.7 37.1 36.5 33.0 at 25° C. in mN/m Particle Size 11 12 11 1150^(th) percentile (nm) Particle Size 17 21 17 19 95^(th) percentile(nm) pH 8.3 8.4 8.4 8.3 Conductivity (mS/cm) 2.27 2.37 2.27 2.24Density, 25° C. 1.014 1.025 1.019 1.018 (g/cm³) Dynamic Viscosity, at1.61 1.46 1.54 1.58 25° C. in mPa-sec Static Surface Tension, 37.1 34.337.2 36.6 at 25° C. in mN/mPreparation and Formation of Aqueous Based Ink Receptive Layer:Application of Aqueous Compositions:

Commercially available, non-primed, impermeable polymer film substrateswere obtained from several suppliers, such as (1) Jindal Films' BICOR™uncoated transparent 120 SLP, a 30-μm clear biaxially orientedpolypropylene film (BOPP) designed for flexible packaging applications;(2) Jindal Films' BICOR™ uncoated transparent LPX-2, a 18-μm, 1-sideheat-sealable biaxially oriented polypropylene film (BOPP); (3) BOPA, aclear biaxially-oriented polyamide film; (4) SM 100 T BOPET, atransparent biaxially oriented polyethylene terephthalate (BOPET) filmfrom SML Films; (5) TRANSPET™ CT1-F from Transcendia, an uncoatedtransparent 12-μm polyester film that is corona treated on one side(BOPET). An aqueous-based ink-receptive layer was formed on each ofthese films. Aqueous compositions used to do this were prepared from thecomponent types and the ingredient ranges described below in TABLE IX.Prior to the coating station, each film substrate was treated with acorona discharge device when required for acceptable wetting at atreatment energy density applied to the bare film surface of 30-80W-min/m². The substantially similar aqueous compositions were applied tothe film substrates using a roll-fed RK PrintCoat Instruments Ltd.Rotary Koater typically by a reverse gravure coating process thatdelivered 5.5 g/m² wet laydown of aqueous composition. The singlestation gravure desirably used a 60-degree hex engraving, 250liter/inch, 14.8 BCM cylinder (100 liter/cm, 23.0 cc/m²). The coatingtransfer efficiency could be varied by changing the ratio of coatingroller to web speed ratio; higher speed ratios gave lower wet coverages.Speed ratios varied from ˜1.0 to 1.8. The coated substrates were driedin-line using hot air dryers that produced a web temperature of at leastabout 40° C., resulting in a dry layer coverage range of 0.45-0.75 g/m².

Each of the resulting ink-receptive media was then either inkjet printedin-line with a full-width CIJ imprinter, or each was spooled on coresfor later sheet-fed printing using 1-inch (2.54 cm) printhead on abenchtop apparatus employing pressurized containers for ink delivery, ora full-width CIJ printhead supplied with pump-pressurized recirculatingink using a fluid (main supply) station. The preferred ink-receptivemedium coverage depended upon the intended aqueous pigment-based inklaydown, and roughly 3.0-4.0 g/m² wet coverage was targeted formonochrome printing, whereas 4.0-5.5 g/m² wet coverage was used formulticolor, high ink coverage printing.

TABLE IX Typical Typical Lower Higher Functional CAS RegistryRepresentative Level Level Component Number Source (weight %) (weight %)Vehicle 7732-18-5 Water 92 86<   Polymer 9002-89-5 SELVOL ™ E 325 3.18.0 (Sekisui SCA, LLC) Polymer 183815-54-5 LUPAMIN ® 9095 3.8 8.6 (BASF)Polymer Not Available POLYCUP ™ 9700 0.4 0.7 Crosslinking (Solenis)Resin Salt 7791-18-6 Commodity 3.3 4.1 MgCl₂•6H₂O Filler 7631-86-9LUDOX ® CL 3.3 5.3 (W. R. Grace & Co.) Wax Not Available MICROSPERSION ® 0.6 0.6 150-50 (Micro Powders, Inc.) Metal 95-14-7 WINTROL ®B-FG 0.1 0.1 Corrosion (Wincom Inc.) Inhibitor Metal 6381-92-6 Commodity0.02  0.02 Corrosion EDTA, Na₂ Inhibitor Preservative 2682-20-4 KORDEKMLX ® 0.0 0.1 (DuPont) Surfactant 66455-14-9 CARBOWET ® 106 0.1 0.2(Evonik Corp.) Antifoamant 125-86-3 SURFYNOL ® 104PA 0.2 0.5 (EvonikCorp.) Antifoamant Not Available SURFYNOL ® AD01 0.1 0.1 (Evonik Corp.)

TABLE X Typical Lower Typical Higher Component Component CoatingSolution Level Level Composition Properties Solution Solution Dry Solids(weight %) 9.5 14.5 pH 6-9 6.5-8   Density, 25° C. 1.04 1.04 (g/cm³)Dynamic Viscosity, at 40-50 160-200 Ambient Temperature in mPa-sec(Brookfield Viscometer using 32-second Zahn No. 4 Cup Time) StaticSurface Tension, at 29 30 25° C. in mN/mSheet-Fed Printing of Aqueous Pigment-Based Inks:

In a representative procedure, the inlet ink fluid line tube of asmall-scale continuous inkjet (CIJ) printing test fixture was insertedinto a 2-liter bottle of inventive aqueous black pigment-based ink K-A(E) in the interior of a steel pressure vessel, and the system wassealed and pressurized to 60 psid (0.41 MPa) with compressed air. Theink fluid line was copiously flushed with aqueous black pigment-basedink to ensure that the new ink was not contaminated by the prior ink inthe apparatus. The fixture consisted of the following elements: (1) apressure vessel fluid system capable of pressurizing the aqueous blackpigment-based ink in excess of 60 psid (0.41 MPa) thereby producing inkvolumetric flow rates through a typical 600-nozzle/inch (236 nozzle/cm)MEMS silicon nozzle plate of about 63 ml/min/inch (24.8 ml/min/cm) ofprinthead nozzle plate; (2) a fluid manifold delivering pressurized inkto a miniaturized version of a KODAK PROSPER® Press Jetting Module dropgenerator to form printing and non-printing drops of aqueous blackpigment-based ink using a 1-inch (2.54 cm) nozzle plate; (3) a dropselection system consisting of (a) a gutter to catch non-printing dropswhen the printer is not printing an image file or when it is notprinting a given pixel even if it is printing an image file; (b) anon-printing drop deflection apparatus creating a deflection zoneintersecting the drop curtain provided by positive and negative air ductassemblies to direct those drops to the gutter, and (c) a catch panconnected to a waste fluid line to remove the unprinted ink, (4) avacuum drum capable of supporting a sheet of porous media (for example,uncoated free sheet paper) or non-porous media (for example, coated oruncoated polymer film) and spinning it continuously at precise speedssynchronized with a control unit to simulate web transport of theprinting substrate in roll form; and (5) a print controller that (a)controls the printing drum speed and synchronizes the drum location inaccord with the data feed to the miniature jetting module drop generatorand also (b) transmits electrical signals to the jetting module CMOScircuitry that renders a raster processed image into pixel by pixel inkstream stimulation instructions using nozzle plate heater pulse patternsby optimized waveforms to generate non-printing catch drops and printingdrops of ink delivered at the precise printing substrate surface pixellocations, as required.

The printing apparatus drum was loaded with a single sheet of inkreceiving medium having an aqueous-based ink receptive layer on a filmsubstrate that was affixed by its back side to a sheet of paper forconvenience in handling and it was printed at 100% coverage full-widthfor about 5 inches (12.7 cm) in length forming a bar pattern at maximumink laydown. The printed sheet was removed and allowed to air dry atambient temperature and humidity, or it was incubated at 60° C. in alaboratory oven for a fixed period of time before testing and furtherprocessing.

Roll-Fed Printing of Aqueous Pigment-Based Inks:

In a representative procedure, the ink reservoir of a roll-fedcontinuous inkjet printing test stand fixture was charged with inventiveaqueous black pigment-based ink K-A (E). Repetitive cycles of draining,flushing, and filling the ink reservoir and fluid lines with Ink K-A (E)were carried out to ensure that the new composition was not contaminatedby a prior ink in the apparatus. The roll-fed printing test fixture wasconnected in-line, downstream from an RK PrintCoat Instruments Ltd.Rotary Koater forward gravure coating applicator allowing the roll-fed,uncoated flexible transparent film substrate to first be pre-coated withan aqueous composition to form an aqueous-based ink-receptive layer asdescribed previously, to be at least partially dried, and then to beinkjet printed using one or more in-line KODAK PROSPER® S10 ImprintingSystems employing a full-width (4.25-inch (10.8 cm)) Stream™ 600 nozzleper inch (236 nozzle per cm) continuous inkjet printhead module enablingeither 600×600 dot per inch (236×236 dots per cm) addressability, or600×900 dpi (236×354 dpcm). The imprinting system consisted of thefollowing elements: (1) a fluid system station capable of (a)pressurizing the aqueous black pigment-based ink in excess of 60 psid(0.41 MPa) thereby producing ink volumetric flow rates of up to about 2liters/min; (b) delivering pressurized aqueous black pigment-based inkto a continuous inkjet printhead drop generator module; (c) returningunprinted ink under vacuum to the fluid system ink reservoir; (d)detecting the reservoir ink concentration by electrical resistivitymeasurement and replenishing the aqueous black pigment-based ink withreplenisher fluid if concentrated by water evaporation, and adding moreaqueous black pigment-based ink K-A (E) to the ink reservoir instead ifit was depleted by use in printing and was at the correct colorantconcentration; (e) providing the printhead with Printhead Cleaning andStorage Fluid to flush the nozzles and duct systems in order to restoreaccurate printing after fouling by dried ink build-up, and to shut downthe system for safe storage over significant time durations; (2) a rolltransport system with an encoder to detect and precisely regulate thetransport speed of the substrate and synchronize a control unit toinitiate and terminate image printing; (3) a continuous inkjet printheadPIC box assembly including (a) a KODAK PROSPER® Press Jetting Modulewith a MEMS silicon-based drop generator to form printing andnon-printing drops of aqueous black pigment-based ink and a Coandagutter to catch non-printing drops when the printer is not printing animage file or when it is not printing a given pixel even if it isprinting an image file; (b) a non-printing drop deflection apparatuscreating a deflection zone intersecting the drop curtain provided bypositive and negative air duct assemblies to direct the non-printingdrops to the Coanda gutter, and (c) an ink return line to the fluidsystem ink reservoir, and (4) a print controller that (a) synchronizesthe web spatial location in accord with the data feed to the jettingmodule and also (b) transmits electrical signals to the jetting moduleCMOS circuitry that renders a raster processed image into pixel by pixelink stream stimulation instructions using nozzle plate heater pulsepatterns by optimized waveforms to generate non-printing catch drops andprinting drops of aqueous black pigment-based ink delivered at theprinting substrate surface pixel locations, as required.

The fluid system used a Micropump Inc. MICROPUIMP® series GJ-N23DB380Agear pump to deliver the ink through a Pall Corp. Disposable FilterAssembly capsule filter, DFA4201ZU0045, containing 0.45 μm nominaleffective pore size ULTIPOR® GF-HV glass fiber media at about 65 psid(0.45 MPa) pressure drop at the nozzle plate, which generated a uniformdrop velocity of about 20 m/sec. The fluid system gear pump speedsetting was continually adjusted to provide and maintain constant fluidpressure at the jetting module to uniformly produce the desired dropvelocity as per the system specification. The required system parametersettings for proper jetting and accurate aqueous black pigment-based inkreplenishment were determined and recorded to a computer file termed an“inkdex” to enable printing on other systems, such as a web press fittedtwo-up with production KODAK PROSPER® S10 Imprinting Systems. Thedeflected non-printing ink drops were caught on a Coanda gutter andreturned to the fluid system ink tank under vacuum. Sustained operationof the printer in catch mode of the non-printing drops resulted ingradual evaporation of the aqueous ink solvent vehicle. Aqueous blackpigment-based ink concentration was maintained to within about 5% of theoriginal aqueous black pigment-based ink concentration by addition ofthe particle-free Replenisher Fluid to it, if the latter became morethan about 5% concentrated based on an ink electrical resistivitydetermination. Test targets were raster image processed to producedigital printing signal instructions for each pixel location at theappropriate transport speed of the test substrate at 600×600 pixels perinch (ppi) (236×236 pixels per centimeter (ppcm)) addressability forspeeds up to about 1,000 feet per minute (303 meters per minute).Various test images were printed at different substrate transport speedsthat profiled system functional printing speed capability using a600-nozzles per inch (236 nozzles per cm) PROSPER® Press Jetting Modulein a production print-head assembly configuration, which produced a4.25-inch (10.8 cm) jet curtain print swath. Operational stability andstart-up robustness (“runnability”) of aqueous pigment-based ink K-A (E)were also noted on this and related test equipment. In order toinvestigate lamination bond strength of printed articles, it was usefulto print side-by-side 1-inch (2.54 cm) bar targets separated by severalinches (or respective cm) among other images. The resultinginkjet-printed articles were dried in-line using hot air dryers thatproduced a web temperature of at least about 50° C. and were wound up inroll form before chopping out segments in sheet form for further testingand processing into flexible inkjet-printed articles.

Formation of Flexible Inkjet-Printed Articles:

A sample of an inkjet-printed article as described above was evaluatedfor image quality and image durability (for example, rub or tacktesting) to qualify it for further testing. Another sample of the sameinkjet-printed article was subjected to lamination to a flexible film bybonding a piece of 3M™ SCOTCH® Transparent Tape, Catalog No. 600 to theinkjet-printed article top surface as it was resting on a solid countertop, using 4-6 passes of firm pressure applied to the tape back sidewith an operator's finger. The tape was then manually peeled slowly awayfrom the sample over 6-8 seconds duration. The tape was observed for anytransfer of inkjet printed image to the tape (cohesive or adhesivefailure), which was optionally quantified by reflection colorimetry.Alternatively, the lamination bond strength was quantified using an MTSSINTECH® 1/G Electromechanical Testing System suitable for uniaxialtensile force peel testing using a 25-Newton load cell and head, andoperating with a delamination draw speed of 270 mm/min rate.

Another sample of the inkjet-printed article substrate was coated withDow ADCOTE™ 577/CR 87-124 two part polyurethane solvent-based adhesivesystem to form a functional layer on the inkjet-printed image of theinkjet-printed article. The adhesive was prepared in ethyl acetatesolvent at 45% solids and applied to the inkjet-printed image using a #4wire wound coating rod on the day after inkjet printing followingambient aging on a benchtop overnight. The adhesive-coatedinkjet-printed articles were dried for 5 minutes at 60° C. in a staticor convection laboratory oven. It was then laminated within 2 hours ofthe oven drying to a coversheet of LD43 low density polyethylene film asa flexible polymeric film to form a flexible inkjet-printed article. Toaccomplish this, the coversheet was first mounted to a piece of posterboard for ease of handling and subjected to corona discharge treatmentat settings of 1.8 KW, 40% belt speed to improve the adhesive bondingbefore applying it to the inkjet-printed article. The two-componentbonded assembly was then passed through a roller laminator apparatuswith the rollers heated to 70° C. and the nip pressure set at 25 psid(1.7 bar), with the transport speed at 0.4 inch/sec (1 cm/sec), tocomplete the lamination and formation of a flexible inkjet-printedarticle. The cooled flexible inkjet-printed article was removed from anysupporting board or paper stock employed to improve its handlingproperties. It was subjected to peel force testing to determine thelamination bond strength with an MTS SINTECH 1/G ElectromechanicalTesting System operating with a draw speed of 270 mm/min rate using a 25N load cell.

Lamination Bond Strength Measurements of Flexible Inkjet-PrintedArticles: Articles Printed with Aqueous Black Pigment-Based Inks

BICOR™ 120 SLP (BOPP) and TRANSPET™ CT1-F (BOPET) polymer films wereused as substrates and were pre-coated off-line with an aqueouscomposition typical of the lower component levels shown above in TABLEIX to provide an aqueous-based ink-receptive layer at about 0.5 dry g/m²coverage on the substrate. The resulting ink receiving media weresheeted, attached to a sheet of plain bond paper for ease of handling,and inkjet printed at 600×900 dpi (236×354 dpcm) addressability asdescribed above. Inkjet-printed articles having BOPET as a substrate and100% coverage side-by-side 1-inch (2.54 cm) width bars were laminated toSCOTCH® Transparent Film Tape 600 as a flexible polymeric film asdescribed above and the resulting flexible inkjet printed articles wereexamined for peel resistance on the same day, the next day, and 4 dayslater using an MTS SINTECH® 1/G Electromechanical Testing System. Theresults were very similar and within the noise of the experimentalprocedures. TABLE XI below reports the 4-day aged data peel forcerequired for flexible polymeric film removal in entries 1-4. Laminationscreening test values of peel force that are lower than about 1 N/cmsuggest that unacceptable bond failure in practical laminationapplications are probable, and values above about 2 N/cm suggest thatfully acceptable bonds will be produced. Examples of the inventionflexible inkjet printed articles in entries 1-2 prepared using aqueousblack pigment-based inks containing water-miscible humectants havingonly two hydroxyl groups and C:O atom ratios of at least 1.0 producedtest bond strengths in excess of 2.0 N/cm. In contrast, flexibleinkjet-printed articles prepared using a traditional humectant in theaqueous pigment-based inks having three hydroxyl groups and a C:O atomratio of at least 1.0:1.0 as shown in entries 3-4 exhibited unacceptablebond strengths well below 1.0 N/cm.

Samples of inkjet-printed articles prepared from BOPP substrates werelaminated using a coating of solvent-based polyurethane adhesive and theapplication of a polyethylene film coversheet as a flexible polymericfilm according to the procedure described above. Entry 5 in TABLE XIshows that aqueous pigment-based ink K-A (E) containing a water-misciblehumectant according to the present invention, having only two hydroxylgroups and a C:O atom ratio greater than 1.0:1.0 produced a good bondstrength of 1.8 N/cm in the flexible inkjet-printed articles comparedwith the exceedingly low and unacceptable value of 0.2 N/cm exhibited bythe comparative flexible inkjet-printed articles prepared using aqueousblack pigment-based inks containing a common humectant having threehydroxyl groups and a C:O atom ratio of at least 1.0:1.0, that isaqueous pigment-based ink K-D (C), shown in entry 6.

TABLE XI C:O No. of Flexible Water-Miscible Atom Hydroxy Polymeric PeelForce Entry Ink Humectant Ratio Groups Substrate Adhesive Film (N/cm) 1K-A (E) 1,2-Propanediol 1.5:1.0 2 CT1-F 600 600 2.4 BOPET Tape Tape 2K-B (E) 1,2-Ethanediol 1.0:1.0 2 2.3 3 K-C (C) 1,2,3-Propanetriol1.0:1.0 3 0.6 4 K-D (C) 1,2,3-Propanetriol 1.0:1.0 3 0.4 5 K-A (E)1,2-Propanediol 1.5:1.0 2 120 SLP Solvent- PE 1.8 BOPP based 6 K-D (C)1,2,3-Propanetriol 1.0:1.0 3 0.2Sheet-Fed Articles Printed with Aqueous Cyan Pigment-Based Inks

BICOR™ 120 SLP (BOPP) and TRANSPET™ CT1-F (BOPET) polymeric films (assubstrates) were pre-coated off-line with an aqueous composition typicalof the higher component levels shown in above TABLE IX to produce anaqueous-based ink-receptive layer at about 0.5 dry g/m² coverage. Theresulting ink receiving media were sheeted, attached to a sheet of plainbond paper for ease of handling, and inkjet printed at 600×900 dpi(236×354 dpcm) addressability as described previously to provideinkjet-printed articles having patches of 100% cyan pigment-based inkcoverage suitable for subsequent lamination tests. Samples of theseinkjet printed articles were laminated using a coating of solvent-basedpolyurethane adhesive and the application of a polyethylene filmcoversheet as a flexible polymeric film according to the proceduredescribed earlier. Peel force strength data were determined and arereported below in TABLE XII.

Entries 1 and 3 (lower water-miscible humectant level) and 2 and 4(higher water-miscible humectant level) show that aqueous cyanpigment-based inks C-A (E) and C-B (E) according to the presentinvention and containing a water-miscible humectant having only twohydroxyl groups and a C:O atom ratio greater than 1.0:1.0 producedacceptable lamination bond strengths ranging from 1.6 N/cm to 2.1 N/cmon the two substrate films bearing an aqueous-based ink-receptive layerof the higher component levels described above in TABLE IX.

TABLE XII C:O No. of Flexible Peel Water-Miscible Atom Hydroxy PolymericForce Entry Ink Humectant Ratio Groups Substrate Adhesive Film (N/cm) 1C-A (E) 1,2-Propanediol 1.5:1.0 2 BOPET Solvent- PE 2.0 Based 2 C-B (E)1,2-Propanediol 1.5:1.0 2 2.1 3 C-A (E) 1,2-Propanediol 1.5:1.0 23 120SLP Solvent- PE 1.8 BOPP based 4 C-B (E) 1,2-Propanediol 1.5:1.0 2 1.6Sheet-Fed Articles Printed with Magenta Pigment-Based Inks

BICOR™ 120 SLP (BOPP) and TRANSPET™ CT1-F (BOPET) polymer films (assubstrates) were pre-coated off-line with an aqueous composition typicalof the higher component levels shown in TABLE IX to produce anaqueous-based ink-receptive layer at about 0.5 dry g/m² coverage. Theresulting ink receiving media were sheeted, attached to a sheet of plainbond paper for ease of handling, and inkjet printed at 600×900 dpi(236×254 dpcm) addressability as described above. The resultinginkjet-printed articles having prints of 100% coverage side-by-side1-inch (2.54 cm) width bars were laminated to SCOTCH® Transparent FilmTape 600 as a flexible polymeric film as described above to formflexible inkjet printed articles that were examined for peel resistanceon the next day, and 4 days later using an MTS SINTECH® 1/GElectromechanical Testing System operating with a draw speed of 270mm/min rate and using a 25 N load cell. TABLE XIII below reports the4-day aged data peel force required for flexible polymeric film removalfrom the inkjet printed articles in entries 1-3. It was found thatdihydroxy water-miscible humectants according to the invention having aC:O atom ratio of at least 1.0:1.0 provided much higher peel forcestrengths than a comparative flexible inkjet-printed article preparedusing an aqueous pigment-based ink containing 1,2,3-trihydroxypropane(glycerol) as the only water-miscible humectant.

Samples of the same inkjet printed articles were also laminated using acoating of solvent-based polyurethane adhesive and the application of apolyethylene film as the flexible polymeric film to form flexible inkjetprinted articles according to the procedure described above. Accordingto the following TABLE XIII, entries 4-11, flexible inkjet-printedarticles formed using BOPP film as a substrate (with an aqueous-basedink-receptive layer according to the invention) and inventive aqueousmagenta pigment-based inks bonded to the flexible polymeric film using asolvent based polyurethane adhesive uniformly and exhibited improvedpeel force strength over a flexible inkjet printed article formed usingthe same substrate and aqueous-based ink-receptive layer using buthaving been inkjet printed using a “comparative” aqueous magentapigment-based ink containing 1,2,3-trihydroxy propane (glycerol) as theonly water-miscible humectant. Generally, the peel force required inthese tests was two to threefold greater for the inventive flexibleinkjet-printed articles versus the comparative flexible inkjet-printedarticle containing the ubiquitous glycerol used often in the art.

In the following TABLE XIII, entries 12-16, flexible inkjet-printedarticles prepared using a printed BOPET substrate bearing anaqueous-based ink receptive layer and using aqueous magentapigment-based inks according to the present invention also showed two tothreefold increase in the required delamination peel force relative toflexible inkjet-printed articles prepared using a comparative aqueouspigment-based ink containing 1,2,3-trihydroxypropane (glycerol) as thewater-miscible humectant.

TABLE XIII C:O No. of Flexible Water-miscible Atom Hydroxy PolymericPeel Force Entry Ink Humectant Ratio Groups Substrate Adhesive Film(N/cm) 1 M-A (E) 1,2-Propanediol 1.5:1.0 2 120 SLP 600 600 1.8 BOPP TapeTape 2 M-D (E) 2-(2-hydroxyethoxy)- 1.3:1.0 2 1.9 ethanol 3 M-H (C)1,2,3-Propanetriol 1.0:1.0 3 1.2 4 M-A (E) 1,2-Propanediol 1.5:1.0 2 120SLP Solvent- PE 3.4 BOPP Based 5 M-B (E) 1,2-Butanediol 2.0:1.0 2 4.0 6M-C (E) 1,3-Butanediol 2.0:1.0 2 2.5 7 M-D (E) 2-(2-hydroxyethoxy)-1.3:1.0 2 1.2 ethanol 8 M-E (E) 2-[2-(2- 1.5:1.0 2 2.6Hydroxyethoxy)ethoxy]- ethanol 9 M-F (E) 1,2-butanediol + 1.5-2.0 2 2.42-[2-(2- Hydroxyethoxy)eth- oxy]ethanol 10 M-G (E) 1,2-propanediol +1.5:1.0 2 2.1 2-[2-(2- Hydroxyethoxy)eth- oxy]ethanol 11 M-H (C)1,2,3-Propanetriol 1.0:1.0 3 0.8 12 M-A (E) 1,2-Propanediol 1.5:1.0 2BOPET Solvent- PE 2.2 Based 13 M-B (E) 1,2-Butanediol 2.0:1.0 2 1.9 14M-C (E) 1,3-Butanediol 2.0:1.0 2 2.4 15 M-F (E) 1,2-butanediol + 1.5-2.02 2.6 2-[2-(2- Hydroxyethoxy)eth- oxy]ethanol 16 M-H (C)1,2,3-Propanetriol 1.0:1.0 3 0.6Sheet-Fed Articles Printed with Aqueous Yellow Pigment-Based Inks

BICOR™ LPX-2 (BOPP), Clear OPA (BOPA), and Constantia Flexiblestransparent polyethylene terephthalate (BOPET) polymeric films were usedas substrates and pre-coated off-line with an aqueous compositiontypical of the higher component levels shown above in TABLE IX toproduce an aqueous-based ink-receptive layer at about 0.6 dry g/m²coverage. The resulting ink receiving media were sheeted, attached to asheet of plain bond paper for ease of handling, and inkjet printed at600×900 dpi (236×354 dpcm) addressability as described above to providepatches of 100% yellow pigment-based ink in coverage suitable forsubsequent lamination tests. The resulting inkjet-printed articlescontaining BOPP, OPA, and BOPET substrates of 100% coverageside-by-side, 1-inch (2.54 cm) width bars were laminated process byapplying a coating of solvent-based polyurethane adhesive with awire-wound coating rod and applying a polyethylene film as a flexiblepolymeric film using heated, pressurized bonding and a laminator inaccordance with the procedure described above, to provide flexibleinkjet-printed articles. After curing these flexible inkjet-printedarticles for two days, the lamination bond strength was determined usinga SINTECH® 1/G Electromechanical Testing System that is described above.The peel forces exhibited by the flexible inkjet-printed articles formedfrom inkjet-printed articles bonded to a polyethylene flexible polymericfilm using a solvent based polyurethane adhesive and OPA film substrateare reported below in TABLE XIV (entries 1-8); those containing BOPPsubstrate are reported in entries 9-16; and those containing BOPETsubstrate are reported in entries 17-24.

All flexible inkjet-printed article samples derived according to thepresent invention, that is those inkjet printed using aqueous yellowpigment-based inks containing only dihydroxy water-miscible humectantshaving a C:O ratio of at least 1.0:1.0 exhibited improved laminationbond strength over the flexible inkjet-printed articles prepared usingan aqueous pigment-based ink containing only a comparative trihydroxywater-miscible humectant (glycerol). For each flexible inkjet-printedarticle, one or more examples of the invention produced a two-fold orgreater relative improvement in bond strength over the comparativeflexible inkjet-printed article, that is a bond strength substantiallygreater than 1.0 N/cm, as high as 2.0 N/cm in numerous cases, and even3.0 N/cm in one instance, assuring the formation of a robust and durableflexible inkjet-printed article. The comparative flexible inkjet-printedarticle never met or exceeded a minimum bond strength threshold of about1.0 N/cm.

TABLE XIV C:O No. of Flexible Water-miscible Atom Hydroxy Polymeric PeelForce Entry Ink Humectant Ratio Groups Substrate Adhesive Film (N/cm) 1Y-A (E) 2-[2-(2- 1.5:1.0 2 OPA Solvent- PE 1.5 Hydroxyethoxy)ethoxy]-based ethanol 2 Y-B (E) 1,2-Propanediol 1.5:1.0 2 1.4 3 Y-C (E)1,2-Butanediol 2.0:1.0 2 1.4 4 Y-D (E) 1,2-Pentanediol 2.5:1.0 2 1.5 5Y-E (E) 1,5-Pentanediol 2.5:1.0 2 3.0 6 Y-F (C) 1,2,3-Propanetriol1.0:1.0 3 0.8 7 Y-G (E) 1,2-propanediol + 1.5:1.0 2 2.6 2-[2-(2-Hydroxyethoxy)- ethoxy]-ethanol 8 Y-H (E) 1,2-butanediol + 1.5-2.0 2 2.22-[2-(2- Hydroxyethoxy)eth- oxy]ethanol 9 Y-A (E) 2-[2-(2- 1.5:1.0 2LPX-2 Solvent- PE 0.5 Hydroxyethoxy)eth- BOPP based oxy]ethanol 10 Y-B(E) 1,2-Propanediol 1.5:1.0 2 2.3 11 Y-C (E) 1,2-Butanediol 2.0:1.0 21.90 12 Y-D (E) 1,2-Pentanediol 2.5:1.0 2 0.8 13 Y-E (E) 1,5-Pentanediol2.5:1.0 2 1.9 14 Y-F (C) 1,2,3-Propanetriol 1.0:1.0 3 0.4 15 Y-G (E)1,2-propanediol + 1.5:1.0 2 2.3 2-[2-(2- Hydroxyethoxy)- ethoxy]-ethanol16 Y-H (E) 1,2-butanediol + 1.5-2.0 2 2.4 2-[2-(2- Hydroxyethoxy)eth-oxy]ethanol 17 Y-A (E) 2-[2-(2- 1.5:1.0 2 BOPET Solvent- PE 0.8Hydroxyethoxy)ethoxy]- based ethanol 18 Y-B (E) 1,2-Propanediol 1.5:1.02 1.6 19 Y-C (E) 1,2-Butanediol 2.0:1.0 2 1.3 20 Y-D (E) 1,2-Pentanediol2.5:1.0 2 0.8 21 Y-E (E) 1,5-Pentanediol 2.5:1.0 2 2.2 22 Y-F (C)1,2,3-Propanetriol 1.0:1.0 3 0.3 23 Y-G (E) 1,2-propanediol + 1.5:1.0 20.7 2-[2-(2- Hydroxyethoxy)- ethoxy]-ethanol 24 Y-H (E) 1,2-butanediol +1.5-2.0:1.0     2 0.8 2-[2-(2- Hydroxyethoxy)eth- oxy]ethanolRoll-Fed Articles Printed with Aqueous Black and Magenta Pigment-BasedInks

In-line application of an ink receptive layer to a substrate followed byat least partial drying and inkjet printing with an aqueouspigment-based ink at 600×600 dpi (236×354 dpcm) addressability wascarried out on TRANSPET′ CT1-F (BOPET) support using the Rotary Koaterforward gravure coating applicator in tandem with two PROSPER® S-SeriesImprinting Systems and dryers, following the general procedure describedabove. After coating, inkjet printing, and drying, the resulting roll ofinkjet-printed article was unwound and chopped into sheets ofinkjet-printed articles, each of which was attached to a sheet of plainbond paper for ease of handling. Flexible inkjet-printed articles werelaminated using a coating of solvent-based polyurethane adhesive overthe inkjet-printed image of each inkjet-printed article followed by theapplication of a polyethylene film coversheet as a flexible polymericfilm with heated, pressurized bonding in accord with the proceduredescribed above, to provide flexible inkjet-printed articles. Aftercuring for at least two days, the lamination bond strength of eachflexible inkjet-printed article was determined with a using a SINTECH®1/G Electromechanical Testing System to peel each inkjet-printed articlefrom the corresponding flexible polymeric film, and the bond strengthresults from use of selected aqueous pigment-based inks in individualexperiments are reported in the following TABLE XV. In entry 1,inventive aqueous black pigment-based ink K-A containing onlywater-miscible humectant 1,2-propanediol having two hydroxy groups and aC:O atom ratio of 1.5:1.0 produced a flexible inkjet-printed articlehaving a lamination bond strength of 2.1 N/cm. In entry 2, inventiveaqueous magenta pigment-based ink M-B containing only water-misciblehumectant 1,2-butanediol having 2 hydroxy groups and a C:O atom ratio of2.0:1.0 produced a flexible inkjet-printed article having a laminationbond strength of 1.7 N/cm. Lamination bond strength values of peel forcethat are near or lower than about 1 N/cm forecast undesirable rates ofbond failure in practical commercial applications, whereas values nearor above about 2 N/cm suggest that an acceptably robust bond has beenproduced for a flexible film based label application, for example.

TABLE XV C:O No. of Flexible Water-miscible Atom Hydroxy Polymeric PeelForce Entry Ink Humectant Ratio Groups Substrate Adhesive Film (N/cm) 1K-A (E) 1,2-Propanediol  15:1.0 2 BOPET Solvent- PE 2.1 based 2 M-B (E)1,2-Butanediol 2.0:1.0 2 1.7

It should be noted that a water-based tie-layer (layer 420 in FIG. 4 )is not required to achieve the high peel forces observed for all of theforegoing examples of flexible inkjet-printed articles listed above inTABLES XI-XV, which comprise the aqueous-based ink-receptive layersderived from the formulations shown above in TABLE IX.

The present invention has been demonstrated above for use in acontinuous ink jet printing system that employs a gas flow dropdeflection mechanism, thermal drop stimulation devices, and nozzleplates fabricated out of silicon. However, the present invention canalso be employed in continuous ink jet printing systems that useelectrostatic drop deflection mechanisms, pressure modulation orvibrating body stimulation devices, and nozzles plates fabricated out ofother types of materials. Electrostatic deflection can be of the typethat includes separate drop charging and drop deflection electrodes orcan be of the type that incorporates both functions in a singleelectrode. The present invention can also be employed in any of thedrop-on-demand printing systems that are compatible with the aqueouspigment-based inks described herein.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be obtained within the spirit and scopeof the invention.

PARTS LIST

-   10 ink-receptive medium-   20 ink-receptive medium-   30 inkjet-printed article-   40 flexible inkjet-printed article-   100 water-impermeable support-   110 aqueous-based ink-receptive layer-   200 water-impermeable support-   210 first layer-   215 water-impermeable substrate-   220 aqueous-based ink-receptive layer-   300 water-impermeable substrate-   310 water-impermeable support-   320 first layer-   330 aqueous-based ink-receptive layer-   340 inkjet-printed image-   350 functional layer-   400 water-impermeable substrate-   410 water-impermeable support-   420 first layer-   430 aqueous-based ink-receptive layer-   440 inkjet-printed image-   450 functional layer-   460 flexible polymeric film or paper

The invention claimed is:
 1. An ink set comprising two or more aqueouspigment-based inks, each aqueous pigment-based ink having at least 75weight % and up to and including 95 weight % of water, and consistingessentially of: a) one or more pigment colorants selected from cyan,yellow, magenta, and black pigments; b) one or more water-misciblehumectants that are present in a total amount of at least 3 weight % andup to and including 10 weight and wherein glycerol is not present or ispresent in an amount of less than 0.5 weight %; and optionally, c) anacidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, and each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in each aqueouspigment-based ink, wherein the weight % amounts of water and the b)water-miscible humectants are based on the total weight of each aqueouspigment-based ink, and wherein when the a) one or more pigment colorantsis a cyan pigment in an aqueous cyan pigment-based ink, the (b) one ormore water-miscible humectants is 1,2-propanediol alone, when the a) oneor more pigment colorants is a magenta pigment in an aqueous magentapigment-based ink, the (b) one or more water-miscible humectants is1,2-propanediol alone, or 1,2-propandiol with2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weight ratio of 1:1 and up toand including 8:1, when the a) one or more pigment colorants is a yellowpigment in an aqueous yellow pigment-based ink, the (b) one or morewater-miscible humectants is 1,2-propanediol alone, or 1,2-propanediolwith 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weight ratio of at least1:1 and up to and including 8:1, and when the a) one or more pigmentcolorants is a black pigment in an aqueous black pigment-based ink, the(b) one or more water-soluble humectants is 1,2-propanediol alone, or1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weightratio of at least 1:1 and up to and including 8:1.
 2. The ink set ofclaim 1, optionally further comprising an aqueous pigment-based inkcomprising any one of a green pigment, an orange pigment, a whitepigment, a red pigment, a blue pigment, or a violet pigment, and thetotal amount of a) one or more pigment colorants independently presentin each of the optional aqueous pigment-based ink is at least 0.1 weight% and up to and including 25 weight %, based on the total weight of eachoptional aqueous pigment-based ink, and the b) one or more water-solublehumectants comprises 1,2-propanediol and no glycerol.
 3. The ink set ofclaim 1, wherein 50% of the volume of each of the a) one or more pigmentcolorants is provided by pigment colorant particles having a diameter ofless than 100 nm, and 95% of the volume of eaCh of the a) one or morepigment colorants is provided by pigment colorant particles having adiameter of less than 150 nm, the particle size diameters being measuredusing a dynamic light scattering particle sizing instrument.
 4. The inkset of claim 1, wherein the b) one or more water-miscible humectants arepresent in a total amount of at least 4 weight % and up to and including8 weight %, based on the total weight of each of the aqueouspigment-based inks, and glycerol is not present.
 5. The ink set of claim1, wherein the b) one or more water-miscible humectants are present in atotal amount of at least 5 weight % and up to and including 10 weight %,based on the total weight of each of the aqueous pigment-based inks, andglycerol is not present.
 6. The ink set of claim 1, wherein each of thetwo or more different aqueous pigment-based inks further comprises,independently, the c) acidic polymer.
 7. The ink set of claim 1, whereinat least one of the cyan, yellow, magenta and black pigment colorants isanionically-stabilized.
 8. The ink set of claim 1, wherein each cyan,yellow, magenta, and black pigment colorants is anionically-stabilized.9. The ink set of claim 2, wherein all of the pigment colorants presentin each aqueous pigment-based ink are anionically-stabilized.
 10. Theink set of claim 1, wherein each of the two or more aqueouspigment-based inks independently has a dynamic viscosity lesa than orequal to 5 centipoise (5 mPa-sec) as measured at 25° C.
 11. The ink setof claim 1, comprising at least one aqueous cyan pigment-based ink, atleast one aqueous magenta pigment-based ink, at least one aqueous yellowpigment-based ink, and at least one aqueous black pigment-based ink,each comprising the (b) one or more water-miscible humectants thusdefined.
 12. The ink set of claim 11, wherein all of the a) one or morepigment colorants in each of the two or more different aqueouspigment-based inks are anionically-stabilized.
 13. An aqueouspigment-based ink having at least 75 weight % and up to and including 90weight % of water, and consisting essentially of: a) one or more pigmentcolorants, wherein 50% of the volume of each of the a) one or morepigment colorants is provided by pigment colorant particles having adiameter of less than 100 nm, and 95% of the volume of each of the a)one or more pigment colorants is provided by pigment colorant particleshaving a diameter of less than 150 nm, the particle size diameters beingmeasured using a dynamic light scattering particle sizing instrument; b)one or more water-miscible humectants defined as follows, and glycerolis not present or is present at less than 0.5 weight % of glycerol; andc) an acidic polymer that is an anionic polyurethane, an acidic acrylicpolymer, an acidic styrene-acrylic polymer, or any combination of thesematerials, each acidic polymer having an acid number of at least 50 andup to and including 240, each acidic polymer being neutralized withsufficient base to render it dispersible or soluble in the aqueouspigment-based ink; wherein the aqueous pigment-based ink is selectedfrom the following: an aqueous cyan pigment-based ink that comprises oneor more anionically-stabilized cyan pigment colorants, and the b) one ormore water-miscible humectants is only 1,2-propanediol, and that ispresent in a total amount of at least 4 weight % and up to and including8 weight %; an aqueous magenta pigment-based ink that comprises one ormore anionically-stabilized magenta pigment colorants, and the b) one ormore water-miscible humectants is of 1,2-propanediol alone, or1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weightratio of 1:1 and up to and including 8:1, and that is present in a totalamount of at least 4 weight % and up to, and including 8 weight %; anaqueous yellow pigment-based ink that comprises one or moreanionically-stabilized yellow pigment colorants, and the b) one or morewater-miscible humectants 1,2-propanediol alone, or 1,2-propanediol with2-[2-(2-hydroxyethoxy)ethoxy]ethanol 1,2-butanediol, at a weight ratioof at least 1:1 and up to and including 8:1, and that are present in atotal amount of at least 4 weight % and up to and including 8 weight %;and an aqueous black pigment-based ink that comprises one or moreanionically-stabilized black pigment colorants, and the b) one or morewater-miscible humectants is 1,2-propanediol, or 1,2-propanediol with2-[2-(2-hydroxyethoxy)ethoxy]ethanol, and that are present in a totalamount of at least 5 weight % and up to and including 10 weight %, allamounts being based on the total weight of the respective aqueouspigment-based ink.